The 4 unit I am buying the seller wants to move to Florida SUPER bad and is carrying back a 2nd mortgage for me.  

Unless you are feeding the cats it is just the way nature is, other outdoor animals like squirells can carry fleas too.

Some states are communal states, so you just have to make sure if the debt carries to your spouse as well.

The developer will carry all the cost to build the homes and split the profits of the home sales with the realtor. 

You could form a single LLC for all properties, which is easier to manage but carries shared risk, or you can create an LLC for each property, which offers better protection at the cost of more administrative work.

Any amount that you are negative carries over and affect your overall Debt to income ratio.

I've been researching whether or not doing a cost segregation study would be beneficial and while I don't think I could use the bonus depreciation for 2022 taxes a recent Bigger Pockets Money Podcast (#360) https://www.biggerpockets.com/... talked about carrying forward the paper loss for coming years and the benefit of doing one now as there is still 100% bonus depreciation which will decrease in the coming years.

But Track Record carries a lot of noise.  

Focus on building strong business credit through timely payments, low debt levels, and solid financial records, which carry more weight than the name alone in establishing creditworthiness.This post does not create a CPA-Client relationship.

The seller will also be incentivized to extend their seller carry if there’s been no appreciation or the building has deteriorated during those 5 years.