Hi there Rocbaroque, and welcome to Mayhem. I have the 48" J class and love every inch of it. Regarding the sheeting loop, I have done mine as a single ended system, which I will describe below. As your sail area is significantly more, you might need a beefier sail winch than my Hitec HS785-HB, but I must leave it to others to advise on that (or chat to Alan Horne, who will undoubtedly have all the answers you need). Also, this is one of those cat-skinning exercises - there are many ways to make this work and mine is just one. That said, here we go -
My main and jib sheets are attached to a traveller that runs along a carbon fibre tube. The sail winch pulls the traveller in, but an elastic return system takes up the slack as the sheets are released. Here is an overall picture of the system outside the boat -

And here is the sail winch end. The winch sheeting line comes off the winch drum, goes off left to the traveller and returns to be made fast in the middle of the picture. You can also see the turning block for the black return elastic.

The traveller is fabricated from PTFE pieces and, while it looks a little crude, actually works very well. The winch sheeting line comes in from the right, round the turning block and back to be be fastened as in the previous picture. The elastic return is fixed to the left end of the traveller. Also fixed there are the mainsail and jib sheets, although only one is clipped on in the picture.

The other end of the carbon tube has a piece of ply that holds the various turning blocks, 2 for the sheets and one for the elastic. You can see the mainsail sheet closest to the camera going round its turning block and off to the right to the traveller. The jib sheet clip is up against its turning block but in action is clipped on the same as the mainsheet.

I hope that helps a little. You also mention the RC system. Assuming you will sheet the main and jib together, as I and most others do, you only need the simplest two channel system to go sailing. That said, even the cheapest systems these days seem to come with plenty of bells and whistles, just don't worry about the frills. You only need 2 channels. If you buy a new radio it should come with a compatible receiver. You will need a sail winch (as mentioned above) and a steering servo. Any standard servo will do, you aren't asking it to withstand big loads. Do connect everything up and play with it long before you install anything in the boat. That way you can understand how it works and can play with getting the connectors in the right slots without having to fumble around under your deck.
Do keep us updated on progress - good luck
Greg