If you create a comp on property A then use that comp to borrow against property B then it seems legal. 

I was reading Brandon Turner’s Book On Rental Properties and in Chapter 18 he said that there will be many things that would come up from tenants that are unexpected.

Luckily, I set aside a portion of the monthly rent for unexpected repairs/issues.

There are lots of ups and downs and unexpected twists and turns. 

In addition to Sheetrock replacement, usually....ac handler, many electrical components, many plumbing components, etc.  

It all depends on whether you want to guess from the exterior, or break laws by trespassing and door knocking.5. the usual unexpected repairs seems like another thing to add.Are you opposed to wholesalers?

I'm not saying that four-plexes are all bad but are usually feel that their future will be perfect and vacancies are painful, especially unexpected ones. 

Each contractor, area, flip, remodel and materials used have different outcomes in the end and as long as you give yourself room for the unexpected you will be good to go.

Any large rehabs are separate, but this could allow you to stabilize your expected cashflow each month, since you won't have to dish out an unexpecte $250 each time someone's drain clogs up. 

If I may ask for some additional clarification, are you saying that my new residence that I'll purchase (or build) needs to have an investment component in order for me not to have to pay capital gains taxes from the sale of my current investment property?