Only downside is Roth IRA cannot roll into a 401k.  

Not sure in your area but 200K should be enough to get the ball rolling. 

SEC Charges Accountant for Role in Mobile Home Investment SchemeADMINISTRATIVE PROCEEDINGFile No. 3-21547August 7, 2023 - The Securities and Exchange Commission today instituted settled administrative and cease-and-desist proceedings against Lawrence White, CPA, the former part-time Chief Financial Officer for Outstanding Real Estate Solutions, Inc.

This is my first purchase (don't want to do anything stupid) and the rents could swing 600/month depending on what I'm allowed to do in the basement - I'd be in the red from a cashflow perspective if I can't duplex them.Am I rolling the dice here / do you not typically find out for sure until you close and begin renovations?  

You can roll the cost of refi into the refinance itself which will limit what cash you pull out. 

Is it smarter to hold onto the house and keep renting it out, or sell now and roll the equity into the new home?

Another approach could be to use LPMI, which rolls PMI into a slightly higher interest rate, potentially saving you monthly PMI payments.

I've been anon lurking for years but am quite keen to roll up my sleeves to learn more.

In a box, $7,200 rent roll on $600k is very good, but we have to be missing some stuff here.

If you have a rent roll that is great.