Some Suggestions

[someotheruser]

First of all, this game is in a great position to be a really unique and fun experience.
And also I know that this is pre-alpha so some of my suggestions are not even relevant because you already plan to address it later in the game.
I will start with the most important to the less important suggestions.

First Suggestion:
The most important thing is, there is almost no point in "ranching" even though its called slime RANCHER. Yeah its pre-alpha, but still I don't see in the current state anything which actually would change this fact.
What i mean, at the moment there is no goal in the game. So i would assume a goal in the game would be: Explore areas, find new slimes. The thing with that is:
I do not have to build a farm to archive this. I just gather all kinds of food while running around and feed it to the big pink slime. After that i gather as many chickens (also by running around) and feed it to the big tabby slime.
Last but not least i run around and gather as many fruits to get for the big blue flying slime(forgot the name). And i would have unlocked all "areas".

TL;DR:
Make either that you have to pay some money additional to the key OR and that would in my opinion the better idea, make the key depending on the plorts rather than the food. For example to get the key from the pink plort, you would need 100 pink plorts to feed to him. Than you get the key. 100 pink plorts could still be easy to gather by running around, but the flying blue night slimes you have to really ranch them. Also you would have to consider the option of feeding it to the big slime and get the key, or make more money first and buy jetpacks and stuff.
The problem in the moment is that there is absolutely no point in ranching(cage in the slimes and harvest the plorts), except you want the jet-pack and more stamina. So you should get they keys in some way by ranching.
Yes at the moment it is even faster to get the key by just building a garden and let stuff grow rather than actually capture slimes.

Second Suggestion:
You should make the slimes itself be worth anything. What i mean is, the whole money farming stuff might be fun for 2-5 hours but at the end this will at some point get boring if there is no point but getting slimes -> putting in the cage -> harvest.

My idea would be that you could "train" the slimes in any way. (Maybe even as easy as make them happy for 2 days or something while in caged in your farm.
Than you could take them out and they would come with you on your journey and would protect you if some slime attacks you. (So there would be biomes where you would get attacked instantly if going alone and you would die very fast when you don't have strong slimes with you to defend you). It might not lead in the direction you are heading, I understand that but than (IMHO) you have to come up with a different idea "what to do with the slimes". For me at least it get pointless at some point to just have the slimes caged in and make money out of it, for the sake of money. I would like to have slimes to do anything for me. Maybe you can also train them to help you on your farm. (collection plorts from other slimes and sell them or put them in a silo, but I would prefer the "guard the player option"),
Also it could be that you train them to different tasks:
The flying slimes for example could be trained to fetch fruits or boxes or whatever from higher up places (especially before you have the jet-pack). The boom/rock slimes could be trained to explode on command for opening secret passages (see "Fourth suggestion).

Third Suggestion:
You probably already thought about it, but still I will add it here.If you have a solution already, just ignore it alright?
At the moment the slime is plorting the second you feed them, no matter how happy they are so i just leave them in the cage until I need money and than they I feed them -> profit. You should consider either making them plort only if they are happy or give them two kinds of plorts their actual plort an a "black/white" plort which all unhappy slimes have in common and which is basically worthless(maybe 1$) or the third option would be, that they just plort if they are happy so not the moment you feed them but just if they are happy.
Also add a "Happy-O-Meter" to the cages which projects the average happiness (or how many slimes are happy, how many are hungry, how many are unhappy etc.)

Fourth Suggestion:
Make a few puzzles in the game. For example you add special kind of "walls" which have cracks in them, and you have to place a boom slime in front of it, and get it to blow up, than the wall collapse and you can reach this "secret section".
Second example: take a rock slime, and when it tries to attack you with its spike ball attack, you just jump to the side, and it hits a special kind of rock, which opens up a hole in the ground to a secret cave.
Or as already mentioned you can train them to attack/explode on command.

Fifth Suggestion
Less of a suggestion more of a balancing issue, the chickens are breading a lot to slowly, i don't know why this is, I might do it wrong, but in my play through i had around 5 tabby slimes (later around 7 boom slimes) and two cages of chickens.
And i never had enough chicken to feed the slimes, I almost daily had to make a run through the wild areas to get enough chickens. I get that you are trying to make meat slimes harder to bread, and i support that thinking, but IMHO your approach needs a little more improvement. I would suggest, that you need a new food for the chickens too. So to feed meat eating slimes you would need: one chicken "cage" and one "hay field" and of course one slime corral.
You might even thing about that one hayfield can feed 2-4 chicken corrals so you don't waste to much space.
Also to make the chicken easier to handle you could separate the cage into 3/4 "sections" the chickadoo-section the rooster-hen-sections,(possibly a egg-section) and the "harvest-section". So new players always know what they can harvest safely, and which chicken are still needed to let the chicken population grow.

Sixth Suggestion
The Farming ground is to small and to "far apart" I love the idea that you can increase the size of your farm by buying new ground. But at the current point its pretty annoying because the walkways are to far apart. At the moment I am always running around and it takes a lot of time from actual farming just to walk over to the new area (the none-cave-one), because in my play through i had the "farm, for fruits and stuff there" while it gets better with time, if you have upgraded your "power/stamina thing" its still annoying. So I would suggest adding a area which is exactly next to the normal farm with 4-6 new building-spaces. Than adding the none-cave-area attached to this. The cave area would be fine, if it had some kind of possibility to grow stuff. I would suggest a stairway to a higher place where there are 2-4 more building spaces, where there would be sun. (I never tested if it is possible to grow plants inside the cave, but i guess if it is possible it is simply because you guys haven't gotten around to implement that they don't grow in the dark).
So my point here is, add more (possible purchasable) building-spaces to the original farm land or right next to it, so at least in the beginning (3-5 hours) one does not have to walk that much.
Also as a side node, plants which only grow in the dark would be interesting.

Well these are my two cents.

On a different note:
Are you searching for assistance?
If so: take the above as an application.
I am a developer, experienced in C/C++, Java, Python, Javascript, C#, OpenGL.
I could also help and translate some of the text(my mothers tongue is not english).
I am Interested in game development for some time now. If you need assistance just message me and we can talk detail and i can show my work, if not, keep up the good work.

I would like some feedback of you guys about my ideas nevertheless

[DeltaStorm]

Walls of text, but good suggestions

[SpiralRancher02]

Actually, the real point of the game is to have a successful, profitable ranch, not to explore all areas. It's why you came to this world in the first place!