Raising capital - It will be difficult to tell an investor their $ is tied up for 30 years and you are only banking on the borrower selling or refinancing.

Quote from @Martin Jones: YouTube gurus will tell you to borrow money from someone else, but that's bad advice for a beginner.

As a investment property lender we saw a lot of success with flips but an even bigger jump in BRRRR success with borrowers holding as long term and short term rentals. 

@Adam Newman you will want to confirm this with the bank but you can’t take a loan out to borrow for part of the down payment so you’ll need to provide all the funds yourself or have a gift from someone for that which you don’t have.If you have a gift from someone to bridge the 20%, that would be ideal.  

Mortgages for LLCs with personal credit under 680 are tough and expensive, and under 640 are typically not really economically practical for the borrower. 

It’s basically an unlimited contribution Roth, with tax free borrowing. 

The key is if someone is lending from a SDIRA to leave reserves in case the borrower defaults.  

Cost of Borrowing: Compare the interest rates and fees associated with a HELOC or cash-out refinance to the hard money loans you’ve been using.

I literally laughed through the phone at his suggestion, because I was broke, in debt, and in every way and unqualified borrower, and the lending environment in 2012 was probably stricter than it had been since the invention of the 30yr mortgage.

As you are partnering with your sister, have a legal document drawn up as to what happens if one of you wants to sell and the other doesn't, how expenses will be split along with money you are putting down, borrowing, profits, etc.