Is this correct?

However, if my recollection is correct, they are mostly in the midwest or south.

What you're explaining, if I read your post correctly, is considered "house hacking." 

However, the information is only as good as the tax knowledge of the person preparing the return.It sounds like you do not have correct financial statements which means bookkeeping needs to be done appropriately. 

If I put 20% down on a conventional 30-year mortgage at 4.25% (the current going rate), the monthly mortgage cost is $2307.This nets me a minimum of $147/month and maximum (with no need to use any reserves and no vacancies) of $668.Am I doing the math correctly?

Should I obtain the HELOC now before a possible market correction (and possible loss in equity) for cost of $1000 or wait to see if I'll need that additional money at all for deal #2.If I buy a property for $200k to $400k that needs rehab, I'll probably need additional funds.

I just spent several hours today correcting a few very incorrect tax returns prepared by CPAs who advertise their services here.

Also, has anyone used any of these other techniques mentioned above personally and if so any feedback would be awesome!  

My assumption is that when you say "Mortgage Payment," you are including PMI, Taxes, Insurance, Principal and Interest, correct?

Am I thinking correctly?