The materials were only about $400.

Natural gas is cheaper that electric , it is what everyone prefers around here .You could always do a mini split heat pump , I have paid between 3 and 4 grand , materials and labor total

Question #2, which is to go one step up to solid materials, such as granite, marble, corian etc...but I am not sure for a smaller unit like a 1/1 typically for a single person, doing that will not bring up my rent even $1, *MIGHT* make the unit more appealing, not sure it's a big factor though, not like  granite on a 3/2 or 4/3. 

Also, if I wait 18 months, then I'll only be able to purchase one property.Mortgage rates are likely to stay low or come down in the medium term and the effects of a recession will not affect property prices materially for years - not in the next 18 months. 

We typically get a premium to the market, which is disproportionate to the cost we incur with the materials & labor associated with the upgrades.

The cost could be way higher due to the use of higher end material.  

He said that he found out his contractor was not paying the subs for the work/materials they did/provided.

Hmm I might have a few GC's in that area, I can def help you source materials for the remodel. 

Once you itemize each repair on the property you need to allocate a price for labor and material for each item to create a detailed estimate for the project.Once you get more experience inspecting properties and estimating costs for your rehabs you can look back at your OWN COST HISTORY and derive your OWN RULES OF THUMB that you can use for quickly evaluating properties in the future.I would recommend getting The Book on Estimating Rehab Costs to help you learn the basics of estimating costs for your projects.

Tariffs and trade wars that have dampened manufacturing generally and raised costs of housing materials specify.