Hey there, me and my brother are wanting to buy a plex, He would be moving into it and using a FHA Loan to get in and i will be cosigning.

You should consider an All-In-One loan for this (I see your comment about the cash out refi).

My primary bank offered me $300k, principle and interest payments only, .09% above prime the life of the loan and an $82 dollar fee. 

If you told him you have been playing pickup games for the past year and need help improving your jump shot, now he has evidence you're motivated and a specific goal he can quickly help you work towards.

Hi all, can I buy a property at the tax sales, pay cash for it, then refinance it into a loan after I own it? 

I would suggest either going with an FHA loan or 5-10% down loan.

if you're looking to get a DSCR loan for a residential 1-4 unit property then the primary borrower/guarantor will be on the loan thus the loan will report on their personal credit report.

In the middle of those two extremes might be a small business with 3 years left on their lease, but they've made improvements to the property that aren't cheap to remove, such as perhaps a dental office (dentists might be pissed that I put them in the mid-risk category, but all the dentists going out of business in 2020-2021 taught us that American consumers apparently regard dental care as an optional and "luxury" spending item). 

30 year fixed, low interest rate DSCR BLANKET loans (put multiple 1-4 unit properties under one loan for cash out or for purchase).Ground Up Construction loans for aspiring developers with NO Experience100% Financing on Fix and Flips (just pay closing costs and prepaid taxes/insurance)Fix and Flip financing that requires no appraisalHELOCS on investment propertiesBuilder's Forwards (for medium to larger developers who want to hedge interest rates on their properties they plan to sell so they can offer "low builders rates").DSCR loans for long term AND short term rentals (I think this is becoming more and more common, but some people have still never heard of this).And so much more!  

Also, I think it will be difficult to not have the buyers try to turn me into a custom home builder if they're securing the loan.