It's now valued at 700k(post bubble burst), paid off, and he rents it out for 3100 a month, a nice additional supplemental income.

My RE goal is cash flow to supplement our income so that spouse can maximize her 401k contributions.

My question is:  does anybody have any experience with a supplemental loan such as this?  

When it’s all said and done I’m just a W2 worker that is trying to get 5-6 properties to supplement my 401k in retirement.

In finance, leverage (or gearing) is borrowing money to supplement existing funds for investment in such a way that the potential positive or negative outcome is magnified and/or enhanced.

I am getting Rich Dad, poor Dad right now.What I meant by looking at REI as a retirement investment, was that we are thinking to have a couple of properties when we retire to supplement our 401Ks and such, when we retire at 60+yo Vs having a bunch of properties for monthly income.

Looking for $40-60k Single family homes to purchase (that requires low to moderate renovation, depending on the price), paying it off before purchasing another, with a goal of buying 1 property per year to startI want to build a passive income portfolio to supplement my income, buy enough rentals to replace my income and hopefully retire early

You can sometimes get a mezzanine or a supplemental loan that is subordinate to the first mortgage, however the rates will be higher than the first mortgage. 

I will be doing some extensive work and not much of the old will remain.I have several alternatives that I'm looking at radiant floor heating, electric heat pump with gas furnace, geothermal heat pump and solar panels to supplement electric or gas heat.I would welcome other ideas, thoughts, pros, cons, etc.

Most big REO offices require a cover page and some other BS.MLS systems have a section for supplemental documents that agents are supposed to download and send with the offer if they exist.