...What other ways can I attract motivated sellers besides yellow letters, for rent signs and ads? 

Also, have to know the local practice on 100 for the garage, and what if someone was not interested... so that income may be tough or a "bonus" for a one year lease to attract a good tenant...

I am an interior designer and we even have to hire a color consultant for every project we do, because it takes experience to have an eye for colors.

Seems like you are at the point where you'd rather turn over management to a designated property manager/management company, rather than dealing with the day-to-day maintenance yourself.

I do not believe the content or design of the postcards makes much difference.  

As a landlord, either way you are in default, you are not as attractive as the applicant who isn't.  

I think LO are very attractive due to what @Matt Huber has mentioned. 

I have several projects going on in Massachusetts and want to be able to design my own floor plans and 3D rendered walk-through. 

Some are more attractive than others for rental purposes, some encourage renters.  

A lousy design, sloppy bill of quantities, or cheap work will cost much much more in the long run than the imagined " saving " at the time of ordering the work.