First of all, it's not an unlimited resource; the Druid can only wild shape twice per short rest, limiting the amount of poison the Rogue can attempt to harvest and by RAW:
DMG p.258
Serpent Venom (Injury). This poison must be harvested from a dead or incapacitated poisonous snake.
Unless the Druid can retain his form after dying, the Rogue won't be able to farm Druid snake venom. Furthermore, the DMG says that harvesting poison requires a check:
DMG p.258
Crafting and Harvesting Poison
The creature must be incapacitated or dead, and the harvesting requires 1d6 minutes followed by a DC 20 Intelligence (Nature) check.
It goes on about how to add proficiency to it and what happens on a failure but the DMG at least says that harvesting parts from creatures is not an easy task (DC 20 is hard, after all)
The point I'm trying to make is that you should allow your players to do clever things but limit the powergamey-ness to a minimum level that doesn't completely break your game. How you do this is up to you, I personally find that, at my table, at least, that doing the "yes, but..." approach to GMing maximizes the fun. "Yes, but you have to make a check to see if you can get enough venom for a single dose (this is important, you can get the vial half full but that won't cut it!). The druid can help you by giving you Advantage on the check, but it's not automatic." Being flexible like this allows your PCs to at least attempt the thing they really wanna do, and fosters a fun game.
As for other possible attempts to exploit "infinite" things, allow and disallow at your own discretion. A good tip for this is to think about how overpowered it would be to allow it.
Take your infinite arrow feathers example, by pulling the feathers off the wild shaped druid (ouch!), he is able to save a whopping 1 GP (What a bargain!). Consequences may or may not exist, depending on the kind of game you're playing but I would personally rule that once the druid reverts, he finds that he lost some of his hair.
Best Answer
Your wild shape forms will have legs (if it is supposed to)
Wild shape allows you to take the form of an animal.
When you wild shape you take the complete form of whatever you are shaping into. The size, shape, and/or condition of your druid before they transform is irrelevant.
So, when you transform into a bear, it will be a normal four-legged bear. If you transform into a snake you will have no legs (as nature intended). Whatever form you choose, you get the normal textbook form of that animal.
Wild shape will not bring the druid's legs back though
However, when you change back, your druid will have the same physical form that they had before they transformed (their "normal form"). Wild shape only allows you to transform into something else for a certain amount of time, it does not have any effects that modify your un-transformed druid self.