I would like to make the jump from my single family rentals to development of small multifamily, but information on the subject is hard to come by. 

The best book I can possibly recommend on the subject is Ken McElroy's ABCs of Real Estate Investing.   

The only concern with that is I wanted to have some higher end finishes in the upper level (mainly appliances and glass enclosures on stairs) that would be subject to a higher degree of wear and tear with a tenant. 

In the situation again the whole sale would be subject to long term capital gains. 

I just started a separate thread on this subject.

The subject property is 4 standalone buildings spread across 6 different parcels of land (3 parcels contain the 4 buildings, and the other 3 parcels contain surrounding land).

These are properties that have sold near the subject property with a similar: build/construction type, lot size, building size, interior condition, property type, year built.

Yes, there are adjustments for the differences between the comparable sales and the subject property (your property), but they are relatively subtle adjustments because they are using "comparable sales".

I use the business line of credit frequently.

Also, if you search the forums for mentors there has been many posts and comments on the subject in case you want to explore others comments.