However, you may have other issues to deal with.

Hi Paul, I'm sorry to hear you are having issues. 

Goals is adding an ADU when remodeling a distressed SFH, but so far none of properties we completed worked for it (zone issues, lot size, garage storage > ADU value). 

Yeah mate,Too much outside influences and logistical issues with new construction.It's much easier/less risky when you control as much of the process as possible and don't need approval from anyone for "this or that".New build works in other markets but why would anyone new build in 43612, 43613 or 43623 for example when they can buy dirt cheap and renovate for much much less than new build.Just my opinion and there are many ways to skin a cat when it comes to real estate investing 

https://www.biggerpockets.com/...12 Frequently Asked Questions (And Answers) About DSCR Loanshttps://www.biggerpockets.com/...8 More Commonly Asked Questions and Answers to DSCR Loanshttps://www.biggerpockets.com/blog/eight-questions-and-answe...What Documents Do You Need for a DSCR Loan?

Should I include security deposits I've received and then forward to my owners in the 1099 I issue them? 

Of course, there are potential issues like alligators, higher flood insurance premium, erosion.

The main issue is that rental rates on the new construction make it challenging to cash flow much, if any, in the first 3 years. 

Other than that, mistakes related to expenses are common, and not electing things like the De Minimis Safe Harbor election, which can save you if you get audited.An option you might want to consider if you do your own taxes is at least have a tax professional review your return after you complete it (but ideally before you file it). 

Bikes from a bike shop will be more expensive but they will be assembled correctly and will have fewer issues.