From years of experience, not in REI, but in online forums, skype chat rooms etc. 

I would suggest leveraging resources like BP and Google in developing your investment criteria, goals, objectives and constraints. 

Just wondering if there's a quick and reliable online vendor, or should I just take my RE broker's advice (I trust her) and use her "guy" (she's never done home equity through him, to me it just sounds like another person who needs to take a cut)? 

Treat this as a normal business transaction, do not even consider this as being family.As for the interest/principal calculation's there are numerious calculators on line.

Buy a rekey kit from Change-a-Lock or Primeline, available online or at home centers.

What are the preferred methods of online lein searching?

The good news is it’s simple math and online deal analysis and calculations make the math much easier and with a greater degree of accuracy

Originally and if money was no object I wanted to go up and back to create a duplex or triplex.

You must understand your goals, objectives, constraints and budget before committing to any purchase (real estate or otherwise).

I read online that a rent increase of 10% or more requires a 60-day written notice.