Yes, you can buy a STVR in your retirement plan.

Could you buy another house hack instead? 

If you are confident you can re-rent it within a certain time frame, you might offer to let her buy out of her lease.

This gives you the financial resources to buy your next property or two.  

If I sell a single family house for $1 million which has a mortgage of $100k, can I do the following: I buy a single family house property using 1031 exchange for $1 million and get a mortgage of $700k .

Many know local dealers and I'd much rather buy from them whenever possible.

For buying a second house, should I declare high taxes again or save for a 20% down payment to qualify for a loan based on my active income, without needing tax returns?

I'm trying to figure out a strategy on buying real estate from the seller (no lenders involved) on payments, adding value and reselling it for profit and thus, paying off the original seller.

Investment Info:Large multi-family (5+ units) buy & hold investment.

The market for buyers on QCD is going to be smaller so you are limiting your market with a QCD but we buy/sell homes all the time via QCD just need to find the right parties.