Given the rising cost of real estate, punitive taxation and high maintenance and operating costs, what can a real estate investor do to cash flow?

Your passive income should be run through an LLC taxed as a partnership or if SMLLC on your Sched E of your personal return as no reasonable compensation is needed and all income will run passive with no FICA/Medicare tax at all.

That allows you all the protection of a corporation and all the tax benefits of Sub-S pass-through taxation. 

There are many advantages of a Delaware LLC, there may be several disadvantages (such as annual fees, qualification, taxation, etc) depending on where you reside vs. where you do business.

@Bo Goebel I second what @Mitch Provost  and Account Closed said about the taxation of your K-1. 

3) What will be my rental Real Estate taxation rules as aforeigner?

Sarah - You made a prior post about wanting to house-hack in NJ.There are unique tax laws when it comes to house-hacking as you purchased a personal residence and an investment property.When choosing an accountant, make sure they are familiar with NJ State taxation as it is one of the more complex ones in the nation.

We don't know what business form would be ideal and how to avoid taxation becoming a nightmare.

And we fought a war with England about "taxation without representation"?

They tax at a 6% ratio as opposed to a 4% Owner/occupant..which usually figures up to three times the 4% and then a couple hundred on top of that.