I am going to help you. Though I am still nursing my morning coffee and as I look at all your question...I'm getting a headache. LOL.
1 - Rewire straight from tone arm to RCA plugs. It just makes it easier to pick cables you like later on. DIN is ok but somewhat limited in cables choices. Its always a better idea to have a continuous run of wire if possible. Try to limit break points when you decide how you want to rewire. Drill holes, no problem. Gauge can vary from 28 min to 32-36. Your choice. The best wire is from Origin Live. It is a little expensive, but you will NEVER need to think about changing it. I forget exactly but I ordered 2 feet and it was little over 100 dollars or so for all 4 runs. Something like that. I can direct you if you like.
2 - Rewiring the power cord is your option. We can go on and on about replacement cords and their advantages. It would make it easier to have a removable cord though.
3 - They sell headlight plastic refurbishing disks at auto stores. They work really well for light scratches and dull appearance. You attach them to a high speed drill (preferably electric not cordless). BUT BE VERY CAREFULL OR YOU WILL BURN THE PLATIC!! This will require practice on spare plastic. DONT SKIMP HERE IF YOU TRY THIS.
One of the biggest tweaks you can do is apply sound deadener (like the kind you can put in car doors for resonance control) inside the plinth body. Killing resonance is the key to good analog reproduction.
Now I have to stop to take a few sips. BRB in a few.