K1s show your share of income or losses from the partnership, and you include it on your respective personal tax returns.Now, to your partners.

I was thinking if I can talk to my neighbor about sharing the cost (I, the landlord, personally provide labor and my neighbor provide material (e.g. fence pickets)).

All the add-ons are a la carte so you can definitely get a lot of value based on what you need.One thing I personally don't like is that when tenants pay rent, they are charged $1 per transaction for ACH use.

I have a salt water hot tub at my personal home.

If I understand correctly; the seller would receive 80% ($40,000) directly from the mortgagee at closing and would enter into a personal agreement with me for the 20% down payment ($10,000) in which he would be reimbursed separately from my mortgage payments at a separately agreed upon rate and term?

I personally wouldnt - I am sure you could use the equity to get more than $600/month in cash flow however that would possibly require some work and risk on yalls end.

I have not done it personally but have some insight, maybe my reply may boost your post to someone with more experience in it. 

When so many renters stopped paying rent during COVID, companies like SureVestor stopped taking new accounts because they were facing a significant number of claimes.I personally don't see it as a good solution.

With that being said, I personally know several people who've had tenants that stop paying their rent and try to hang around for as long as possible. 

I am not sure what type of real estate investing you're considering, but it sounds like, with your family and busy job, you won't have a lot of time to be hands-on or personally involved.