Hi Nick. Ill answer these questions as best as I can, anyone can chime in. I'll also encourage you to verify these on your own as well.
LLC: 1. You would want to go through a RE attorney or CPA, ive heard of both doing them, but you ideally consult with both to find the best entity for your situation.
2. Each partner should have their own LLC or sole proprietorship and all 4 should combine to form an LLC for the deal. So 4 LLCs with ownership of another.
3. I belive you would get depreciation with partnerships (individually for sure), yes. That I would double check.
Operating:
1. You can Google good examples.
2. These should be as detailed as possible. Stating equity and cash flow share, each persons roles within the deal, how the profits AND the losses are split. What happens when people don't do their part, what happens when another member dies ect.
3. This should 100% be check by each individuals lawyer to make sure its in each individuals best interest.
I hope this helps, again verify everything im saying always.