Don't let your scepticism interfere with your opportunity to learn new methods, techniques, and strategies.

although they both are interdependent.The best way to understand costs is to get a Floor plan drawn and get quotes from at least 3 people in the area who have done ADU'sIt's always a good idea to involves a professional right from the start, especially someone who is experienced as they will suggest techniques that could bring value and save money in the long run.

I justified selling my house to buy two as using the stacking technique.

The technique is called a 1031 exchange or a like-kind exchange.

So what’s the technique used for discovering there’s a secret extra tenant living there?

Is there any other techniques that is more better vs another to examine repair/rehab cost while analyzing property.Hope to get lot of stories n ideas from you guys.

we do a lot of infill building.. this only works in HIGHLY desirable areas @Wayne Brooks  as Wayne states not sure were your thinking the value play is here.now there are plenty of folks that buy cheapo lots in FLA like Lehigh acres then sell for a few grand more on contracts those are the land flipping guru's you see that's what they teach.. and there are millions upon millions of lots available for this type of activity generally in FLA  and West Texas  AZ CA and other areas that had massive land speculation booms in the turn of the century.. think Lancaster Palmdale in CA there are million plus platted lots there that get traded around at tax sales every year.to find land with value to builders you need infill in established areas.. close to down towns.. in areas that are regentrifying .. lots that have shadow plats beneath them. or you can split using a lot confirmation technique ( common in Portland)  you need to work areas of Scarcity .. 

The problem was that after I made that down payment of about $45,000, I had very little money to keep expanding.I had to use multiple lower money techniques in order to grow over the years including:-401K loan for down payments on three properties-FHA owner occupied 4 plex with 3.5% down-Conventional mortgages with 5% down on 2 single family homes that I owner occupied and later turn into rentals-BRRRR method on one home to get all my cash back and buy another propertyThe next thing I'm doing is either refinancing or selling a property in order to get way more units.

That surface will survive practically any cleaning technique and, undisturbed, there are of course examples that have lasted millennia.As far as I can tell, grout removal and replacement was not really given to you as an option to deal with the problem.

Try to concentrate on house-hacking technique to digest more before you purchase your first deal.