(he's a millionaire and self-employed). 

Share what age you retired and if you have not retired, share what age you plan to retire.Well, since your definition of retire is leaving W-2 employment for full time RE then 23.

I have been reading a few posts on BP forums (that are 3-5 years old) about self-employment taxes which state that if your average stay is less than seven days then you need to pay SE taxes, no questions asked.

I would be interested in being able to contribute to a SEP IRA or Self Employed 401K.

I was thinking it could be a value add having the ability to see the story behind a tax return for self employed folks.

If you don’t really know the market, surround yourself with people that do and start learning about cap rates in that market, vacancy rates, rental growth rates, unemployment rates, employers (job generators), governmental policies and regulations, and so on.

What exit strategies they have employed and what is their niche in real estate.

Your CPA can do this but they must ensure they follow the IRS guidelines and either employ or act as an independent third-party certifier.Can I apply for this deduction regardless of how much I spent on upgrades on the building?

Profit from flips are taxed as active, ordinary income which includes self-employment tax (15.6%). 

You get that first paycheck and notice your employer automatically took out a portion of your salary and create you a brand-new 401K account.