Does anyone have any tips on the best way to finance renovations/improvements for properties like this?

Interest paid on acquisition indebtedness and home improvement indebtedness is generally eligible for the deduction.  

YouTube has a lot of great videos for this. 

His name is Marco Carbajo - I would google him and see his videos on YouTube, etc...

If they are below market rent, that is OK as long as there is room for improvement and tenants won't be an issue.

My plan was to buy, improve a bit (house was not in bad shape, just need some TLC), and rent out and hold at least 2~3 years. 

We stuck it out over a year hoping things would improve but they have not. 

That’s the second-straight month of index improvement, and it’s been driven by — you guessed it — lower mortgage rates over the past 4 months.

Selling (1031 exchanging) our high equity family owned properties is the best (really only) option that we have for funding our share of new purchases right now and with each new purchase, we are buying nicer and usually larger units in better neighborhoods so I'm trying to improve the quality of our family owned holdings in addition to growing a new business with our new partner.

I believe it's actually a very good regulatory environment now that the permits are in place.Overall, I expect metrics to continue to improve over the next few years as the demand for STRs continues to grow in our market at a 15% year over year rate.