Newbie questions: equity, ppl I need...

[Sheree H.]

I'm super new at RE and have to look up almost every single acronym you guys use, so please bear with me if my questions are mind-numbingly basic. I searched and read about equity, subject-to, and attorney, I have about a million tabs open, and I still don't understand!

First, I don't understand how equity fits into forming an offer, specifically using this formula I got from a "guru" for buying/rehab/selling subject-to:
Property MUST HAVE at least 30% equity. Then, ARV * .65 - repairs = offer price. Offer price - back payments/fees - loans = what owner gets.

What is the purpose of having at least 30% equity? Does it make a difference that the "guru" lives in SoCal, while I'm in GA?

Also, what is wrong with my math? I'm obviously not seeing something here.
An example property I'm researching:
ARV = 200,000 (low estimate, comps selling 202k-212k)
Equity = 60,100
So my offer = 200,000 * .65 - 30,000 (low estimate at $10/sq ft) = 100,000 ??
If I understand correctly, he still owes 140,000 on his property, and my offer of 100,000 is waaaay lower than his loan. This won't even cover his loan, much less his back payments, and basically he's going to have to pay me to buy his property. I am very confused.

Finally, to do a subject-to/rehab/resell, do I need both a RE attorney and a title company, or is one enough? I'm going to contact an attorney to walk me through steps / contract papers, and his website mentions doing title insurance, title searches, and reviewing title reports, etc, so why would I need to look for a title company also?

Thank you so much!
Sheree in Atlanta