I currently self manage my properties using Buildium and I love it especially the resident portal and ability to accept ACH rent payments.

Depending on what the line looks like (i.e. if it's just a small gap in a joint/imperfection in the line that the roots are growing in, and not that a whole section of the line has collapsed or anything like that) then you can probably try this first before replacing the line.

I have 2 separate Property owners where im located in Maine both looking to do joint venture deals where they provide the land and I get the project lined up and funded.

Most leases make tenants like this "jointly and severally liable" meaning they are BOTH responsible.

are they filing tax returns jointly or "married filing separately"?

Thus, as I am at this point a ‘hobbyist’ and not a professional I presumed I would simply report whatever minimal profit or loss realized on this first joint flip project as pass through income.

Please make sure you vet your partner properly, I wouldn't recommend doing a joint venture or partnership with someone you don't really know. 

If you are able to connect with others who are invested (such as through this forum), perhaps a group of you could get together to file jointly, and split the cost. 

Potential outcomes include develop and hold/rent, lease to developer, and joint venture.

Section 121 Exclusion: You’re also eligible for the $500K exclusion (if filing jointly) under Section 121 since it was your primary residence for two of the last five years.