Welcome, Nick.
Wiring for DCC is literally as simple as wiring a heavy gauge power bus that more-or-less follows the main run around your layout, but below the bench surface, and several thin gauge wires feeding the rails at necessary points to maintain the signal strength of the DCC system at all locations.
So, picture two 14-16 gauge wires in a loop around the layout you describe. They don't need to actually close to a loop; you can leave the ends tacked up and capped near their origin if you wish. At intervals of anywhere between 3-6', you would run a pair of 20-22 gauge wires soldered to the bus and up through the decking to the rails. Where turnouts at each end of a spur will cause a short if designed to route power a certain way, you can just leave gaps at each end of the spur, before the turnout, and run a pair of feeders up to that segment oriented the same way as the track polarity beside it.
If your older engines run well, you may be able to convert them, but chances are very good that you will have to isolate the motor from the frame entirely. Cut all leads to the motor terminals and also ensure the casing doesn't make contact anywhere with the metal frame. Only the decoder should have electrical contact with the motor. I don't know enough to go on...you'll get the help you need here. But wiring for DCC is very simple, provided you know when to gap and when to feed the rails. Soldering all joints may not be the best idea...you should leave some joined with joiners and with a slight gap that can open and close to help the tracks adjust to movements due to humidity in the wood below them. Solder most, sure, but leave every third or fourth able to slide. Make sure the tracks on either side of the sliding joiner get their own pair of feeders in case the joiner eventually stops providing continuity.
That's about it!
BTW, if you have never had a helix. they take up scads of room, and they can't be very steep or very tight. Most folks use a long grade called a no-lix to get to a higher level. A helix is just a huge blob, and you have to have a lot of space to take advantage of one.
-Crandell
Hello
First a little intro my name is Nick I have always like model train had a couple plywood layout (4' by 8') when i was younger now that i have gotten a place where i control whats in the garage i have started a new layout my first real layout. The scaleis HO and i have some of my old trains left so it was helped my decision. So i'm going to model my home town of pheonix and BNSF the layout is 12.5' x 17.5' rap-a-round with a penninsula in the middle its double decker and a helix with some staging and storage on the lower level. this layout is going to focus on yards and industrial areas. my last layout had the old dc controls i plan on using dcc but i'm not sure how to wire the track and where i need to insulate joints and how often to conect track to the bus and if i need to insulate between contections? and i'm soidering all non insulated joints. thanks for any help nick