The first thing that you need to do is make 2 or 3 holes in all of the girders for wire pulls. A speedbore would work nicely now and whatever you prefer to chamfer the edges quickly.
This will go against the grain, but a bus system work fine with any control system.
Use 12 position terminal blocks and get some jumpers when you buy them. Purchase 500' rolls of 14awg and use that for the bus and power feeds to keep it cost effective.
Pull the wire through the holes with the roll on an axle for the entire layout.
A color will be needed for at least 8 positions or 8 colors. This should handle your needs for track power and accessory power of multiple voltages. That will leave four positions open for jumpering or special needs. Easy enough to do later under the table.
next, cut in about every 15' and strip and crimp terminal connectors on both sides and attach them to a terminal block.
When finished and you install the deck, you will only need to screw each terminal block to the deck.
prior to installing the deck, continuity tests can made to confirm good connections.
Chicken wire should be stapled to the bottom of the helix levels. This will be for an earth ground plane for the Legacy/TMMC signal separation.
You can email forum members aubv, Tom Tee, and Elliott with questions also. aubv (Brian) and Tom build layouts professionally. Elliott's builds are of the same caliber.
There's a lot of why's, how comes? and becauses, but this is like the power company's power poles and wires. It's a distribution system from the power source. What it supplies and how doesn't matter at this point.
I said against the grain to begin, because this does work for both DCS and Legacy. proven by many builds by various folks. The details can come later.
When you arrive at the build the power and control panel stage and the connect the track and accessory stage there are more tips and pros to look at for help.
That's my 2ยข, which I believe answers your question.
