Need advice on a 2nd primary and what to do with force appreciation

[Tony Pham]

So I have a primary residence now that I bought back in 2020. It has 3.125 percent and I’m sitting at about 100k in equity on that property. 

Now fast forward 4 years, I found a potential good deal in a way better neighborhood that the wife and I want to move to. It's next door to her mother's house. The seller wants to do a private sale(yes I have an inspector and contractor on hand). He wants to sell for 300k but willing to negotiate. His has has 2 bed, 1.5 bath but has an unfinished basement which I'll be adding 1 more room and 1 more bath. Comps in the area are saying I'll probably get around 450k ARV.

Now with that said, after i cash out refi, how do I get into more real estate? I’d probably need money for a down payment and more money for rehab as well. I’m not too familiar with cash out refi and how much I’d get back and all the ins and outs of that just yet.

thank you in advance