It can take a year or more to complete an ADU.

If you can get a note for 200K at no interest and you have completed your due diligence on this deal, then go for it. 

You'll need money for: closing costs, down payment (if any), operating capital to get the construction/rehab started (most HMLs reimburse you in draws for the work completed), along with some liquid reserves on top of that.

We are a small partnership with 4-5 properties currently, but we are growing and hoping to find a reliable lending partner that we can do repeat business with.About 3 months ago, we successfully completed a BRRRR deal where we had excellent numbers, over a 1.25 ratio at 75% LTV, our guarantor partner has an 800+ credit score, and we had no issues qualifying for the loan.

Incidentally, I cancelled last year when it auto renewed as well - I guess I've got to completely delete my profile and close the attached credit card for a cancellation to stick?

If you can raise money without stressing out completely, than go for it.

There are a few that do not have any seasoning requirement on a cash out refinance as long was there was rehab completed on the property.

There were a lot of costs that we didn't expect like the plumbing had to be completely redone.

In the end, the project was completed successfully and sold for a profit.

Your concerns are completely valid.