I figured a foundation repair would be like any other big item repair: just find a good contractor, pay the money, and get it done. 

I have a low credit score (slightly above 600) due to carrying high credit card debt as well as having some charged off CC's from my college days, however the statute for those to show up on my credit report expire in August of this year so it should provide a sizable boost to my credit score, in addition to my plan I have in place to reduce my total credit usage from $12,000 (out of 13,000 available) down to about $4,000 by July (hopefully lower!).  

@Carrie Huie Indoors I have used wood and outdoors powder coated metal.

I would suggest a few items: 1) Ensure you have cash on hand to make payments on the HELOC during the project, 2) Try and find a HELOC product that only requires interest-only payments (therefore reducing your payments during the project, 3) Build in some cushion on timing of the renovation and sales process for the flip in case either takes a few months longer.

If a property clears these hurdles, I’ll then start to dig a little deeper.If you're looking for "what line items should I use" when calculating expenses, just go to the BP calculator and see what they ask for.

ADU square footage cannot be included in the GLA in the appraisal grid and must be an added line item at the bottom of the grid.

My units are larger 3 and 4 bdrm townhomes, 1600-1800 sf each, intended to serve families.With a mid-range construction budget, what items are worth splurging on to get improved rents? 

@Adam David GraningThere are a lot of different guideline variances on these depending on the lender they go to and they've gotten much better than they were just a few years ago, but for the most part, you can get 75% cash out with rates in the 4's and low 5's on a 30 year fixed with no income verification.These loans carry a prepayment penalty, require all properties be appraised, require each property in the proposed portfolio to have a value of at least 75K and require the property to be stabilized (no renovation and leased). 

It's equally as important to go over the loan estimate together with the loan officer and have them explain each of the line items.

As mentioned above only some of the renovation will qualify for bonus depreiation, but costs will carry into the year the property in placed in service/ available for rent.