Is making a healing poultice equivalent to a healing spell easy, medium, or hard?
1 day, 25gp, no check required. XGE page 130
Is finding ingredients for an antidote easy, medium, or hard?
DC 15 XTE page 82, although Iwould adjust this for terrain (harder in desert or ocean, easier in forrest or jungle, impossible on Avernus or in the lower dark)
Is foraging a cure for a disease easy, medium, or hard?
I don't think there is such thing that cures disease in 5E. You need lessor restoration or lay on hands for that. Also there was no real life anti-biotics in the middle ages, so I don't think there is an argument that there should be a non-magical way to do this.
That is not to say you should not homebrew it, I would start with rules for crafting a scroll of lessor restoration and go from there.
Is crafting improvised weather gear or traveling gear for natural enviroments easy, medium, or hard?
DC 10 or 15 covered on XGE page 81 or 83 or 85 depending on what gear specifically you are talking about.
Is calming a wild aggressive beast easy, medium, or hard?
Depends on the DMs call and what you mean by aggressive. This is a bit silly, it is like asking how hard is it to row across the river - well is the river the mississippi or is it rapids.
Is taming a nonhostile wild beast easy, medium, or hard?
You can't put a DC on a question like this. It is like asking how hard is it to persuade someone. Persuade someone to bum you a cigarette - probably easy, persuade a cop to let you go-hard, persuade a king to give you his kingdom-impossible
Considering this. Wolf Cub - Easy, Elephant-medium, Rino-impossible
Is making a makeshift ghillie suit or other camoflauge easy, medium, or hard?
I would say this is disguising yourself to look like surroundings and as such give it a DC 15 from page 81 in XGE.
If concentrating a bane poison easy, medium, or hard?
etc etc
Poison is covered separately, basic poision can be created with poisioner's kit, or you can extract other poision from a creature with a DC20 check. Concentrating a poison is not something that can be done RAW.
Every DM will give you different answers becuase the game designers didn't and the community never made a lick of consensus.
The game designers addressed most of these things explicitly and what they didn't the DM is supposed to make a judgement on.
Further having rules does not mean every DM won't do it differently. Most of the DMs I have played with have different rules for Mage Hand Legerdemain and none of them will allow my Arcane Tricksters to use Mage Hand Legerdemain explicitly RAW - Specifically they don't let me steal things off of enemies in combat as a bonus action and they don't let me attack then then pour oil on another creature as a bonus action every turn even though the rules explicitly say you can do this. Some of them make me string several turns and bonus actions together, some don't allow it all and some allow it but alter it (so the oil does not light automatically when hit by fire damage).
For this reason it is kind of silly to make up hard and fast rules for all these things.