It won't be perfect of course, but it will be a step up from the laissez faire system (or lack thereof) that we've been using in the past. 

Generally, the properties that benefit the most from a cost segregation study are properties that are remodeled, expanded, purchased or constructed after 1987, the year in which the Investment Tax Credit was enacted.

and how well my credit score will be?

A good indicator of this would be analyzing the HUD Fair Market Rents year over year.

Your best bet for that size will be local banks and credit unions, good luck.

We have credit scores over 730 and have been "soft approved" for around $750k. 

The seller doesn’t need to know that the underwriters may give you more of a hassle than other buyers.Or do you have lines of credit or a private lender so you can make a “cash” offer then try to get the financing through before close or at worst just do a cash out refi after close?

I'm looking at investing in a short term rental in Jacksonville, my budget is fairly modest though, up to $300k so I'm not looking to do a high-end STR.

He was helping a friend in a weird situation but $700 was fairly close to what others rented for.

As mentioned seller credits are the best path as title insurance and taxes are pretty much fixed.