Even under this scenario, with a 50/50 split, you will not be getting paid for doing all the work.Another option would be for you to put in 50% of the purchase price using an LLC that you own 100%, borrow the remaining 50% from your investor as a 2nd position loan at a fair interest rate with points, and borrow the rehab under your personal guarantee.Better, if you can find a lender who will lend to a newbie, and they are out there, you could borrow the purchase money using some of your cash as a down payment, as well as all the rehab funds using a construction loan.

(Floating rate loans, with no rate cap) 

If the seller will entertain it you write it into your offer - what you're willing to pay total, loan term, interest rate, down payment. 

Wanting to explore other options or find out other financial strategies for trying to build a detached home on our lot without having to refinance out of our 2.75 interest rate with a cash out or doing a HELOC.

My mentor says you can get more cash flow and liquidity with SFH vs Multifamily, since brokers seem to want a certain cap rate on sales accross a geographic area vs when working with SFH sellers, they're more flexible and motivated based on individual needs.What are your thoughts on buying SFH vs Multifamily?

I normally purchase very cheap homes, remodel, refinance and rent.

Last I did their rates were 1-2%. 

and unfortunately, with rates and prices high, it has just gotten very, very tough to cash flow on long term rentals.i browsed a few other threads you started and it sounds like you already own your primary residence and are looking to get started in investing. 

Would a bank(say like BankofAmer) allow me to assume the low interest rate of another property and blend the interest rate with my current rental property?

You’ll get an automatic 20-40% discount (tax deduction) off the rates which might make doing it yourself not worthwhile.