New install

I bought a used columbia glider and the coax and antenna combiner have been modified and nothing works. I would also like to move the radio up into the upper console. the local parts supplier sells antennae kits with 2, 3 or 4 ft fiberglass whips mounts and a "cophased" coax cable. I will need to cut the ends off to fish it thru into the doors and resolder new connectors on.
Questions.
Do I shorten the cables or do I keep all the length and hide it?
Is 3ft better than 4ft?
If I have good continuity thru the mirrors to ground should I still run a gound wire?
Thanks.

 

The only ones they have have the permanent installed connectors I'm ok with soldering new ones on. So leering all the wire tied up somewhere is better?