How close to rear of speake for a rack?

Not at out at all sure why you are trying to shorten your cables. General view is that an 8-9' length of speaker cable is optimal and also getting your rack out from between the speakers will help with imaging

in my setup I use a 25' interconnect from pre to my monoblocks with the pre and sources all off on the other side of the room. I use 8' speaker cables and cross them up front.  

In any case the further you can get the big rack, and especially the turntable, away from the speakers the better

Some of us do not have the luxury of having lots of space. In my case, I’ve taken lots of measures to isolate the stand and turntable from vibrations...
- the mass of my turntable is pretty high and has sorbothane suspension in the ball bearing feet
- the shelf it sits on is a sandwich of granite on top of 3/4" MDF, with a thin layer of foam between them
- the shelf itself is isolated from the frame by small sorbothane pads
- each shelf is isolated from the next by spiked feet
- the "interface" to the hardwood floor is inert rubber blocks with small felt pads

Each component has ball bearing feet and sits on its own granite/foam/mdf sandwich shelf

I can’t say its perfect, but I don’t believe any component suffers from vibration. None that I can feel anyway :

My rack sits 8" to the left of my right speaker and 6" back from the front of the speaker

regards