Hi Everyone,
No need to over complicate things. 
Our transformers can run multiple buildings (as noted by above).
We have 3 sizes of transformers available. For your purposes, I suggest using some of our bigger 5-Amp model (SKU# 279-4050), as opposed to the 1-Amp or 3 amp models.
However, some buildings take a lot more power than others. For example, the World Headquarters building takes much more power than the Melrose Park train station. I've tried to my best to indicate the approximate power draw for each building on our website. This can help you as a guide.
Remember, the electronic signs (which are little computer boards) are the most sensitive components. Anything much over 4.5 volts or not very "clean" current will ruin them quite quickly.
The best idea is to use our transformers. If you do use other power sources, you use them at your own risk. We believe, unless you are pretty much an expert, it's just not worth the risk.
The simple, cheap answer to a single switch are power strips (as mentioned above). Add extension cords in between and you can put them wherever you need them on your layout.
Be safe, have fun and stay well!
-Mark the Menards Train Guy
