Tube Integrated on Shelf w/Center Ch. Speaker

It's best to isolate tube gear from vibrations as much as possible but this can be difficult or expensive to do. One thing you might try is to download an SPL meter for your phone or tablet and then place some test tones or even just music with a consistent volume. Move the phone around the areas your tube gear might be placed and see what readings you get. At the very least, if you can keep it out of an area with peak SPL, that would help. My two cents.

You are probably OK with that set-up. I would not worry about it. You can always change it later if you want, or not. 

You do want to isolate tube it can be as simple as sorbothane pucks but you don't use them at the same time it won't be from the center channel