I would look for a bunch of Sub To Deals with 2-3% interest rates ...... then rent out for cash flow and huge equity build up when rates are really low (check out amortization schedules and compare 2-3% vs 6-7% with the same balance and length of time - check out the principal portion each month - the lower the rate the higher amount goes to principal PLUS better cash flow).

You could just let the money build up in your checking account.

Been in IT for 20 years, looking to put my skills to work to build up my retirement.Chris Welcome to BiggerPockets!

Now, if $50k is all you've got, I suggest you build up at least six months of reserves before diving into a deal like this.

The reason being I have to build up my credit score before I can get approved for a loan. 

@Dorian Gray - I think part of the answer to your question depends on the likelihood of needing more funding in the future and if you have another plan to slowly build up reserve funding.

I personally started investing there in 2019 with a budget not too far off from yours, and I've been able to build up a portfolio of 12 doors since then, which now kicks off over $16,500 in gross monthly rents.Detroit has a lot going for it—affordable price points, strong rental demand, and good opportunities for cash flow, especially with single-family homes and duplexes in certain areas.

Envelopes, paper, ink, etc.I planned on 6000 pieces per month.  

This could let you start building relationships with others in your area (and potentially lead to joint ventures later) and to build up your working capital.

Purchasing subject to allows you to (1) buy a property and pay a lower rate (3-4%) that was in existence when the loan was originated, so cash flow will be better as well as equity buildup; (2) not have to qualify for the mortgage saving time, expense, and allowing property purchases in greater number than otherwise and (3) no personal liability on downside (4) no debt added to your PFS.