Interconnect Length

Are you connecting the phono cartridge directly to the phono stage of the pre-amp, or are you connecting to the output of a seperate phone stage?

If the former I agree with the comment about 3ft. If the latter you could stretch it out a bit, but still wouldn't strech it out to 20ft. I keep all of my IC's no longer than 10 ft and use 3 ft when possible.

THanks for helping - I don't even know what cartdrige I would use - I have not touched nor consider getting a turntable since I am 14 years old... I am out of the loop. 
All I know is that I would use RCAs into my integrated, and I would place the turntable on a dedicated stand, to avoid all vibrations from walking and playing the sub on hardwood floor.
Maybe I could place it on the left corner of my room... (see my room in virtual systems).

Is it possible to mount your TV on the wall? That way, turntable would fit on the component stand.

Low capacitance cables should be okay! 
https://www.bluejeanscable.com/store/audio/index.htm

Don't put your turntable in a corner -- this is a bass node and will maximize interference with your table. Ideally as others have noted the cable to the phono stage should be as short as possible.

One option to consider is getting a small phono stage that you locate next to the table connected by a 1M cable - then run a longer cable from the phono stage to your amp. Of course your amp has a MM phono stage built in so you could go with a head amp and a low output moving coil and the run the longer cable to the Marantz. Even a step up can help -- I currently run 2M cables to my step up then another 2M to my phono stage and have no issues