You've got lot's of planning ahead...
I'm in the process of wiring up my RV-7. I'm thru about 60% of the wiring so far. I have quite a bit of avionics: Dual AFS 5600's, Dynon D10A, TruTrak Vizion 385 w/ auto trim, Garmin 240, 650, 255A, 330-ES, AeroLED wingtip lights, Nav/Strobes, Dynon regulated Pitot Heat, defog fans, seat heaters, panel and map lights, boost pump, P-Mags, Plane Power 30A backup alternator, ADS-B, ACK ELT, etc. Search the forums and you can see a CAD model I made of my instrument panel.
I've got 34 pages of wiring schematics. All of the wires are labeled with a code that matches the wire on the schematic and the wire "function" to make future troubleshooting/modifications easier. I broke the schematics down by sub system. I'm running all of my ground wires to a forest of tabs located on the inside of the firewall (P-mags and a few other engine related items have a local ground). To get a handle on how much wire I would need and how to route it I first ran string for all the wiring. It was cheaper and quicker than using actual wire. It was a good thing I did since I changed my mind 4 or 5 times during the string running due to figuring out better routing. I measured the length of every string and used this to purchase my wire. Of course I purchased a little bit more just in case. During my wiring process I've been measuring the actual length of the wires and updating a spreadsheet that has all of the wire lengths and other info I need to wire this thing up. The difference between the string lengths and the actual wire lengths have usually been within an inch or two. Most of the time, almost exactly the same. The nice thing is I'll have actual numbers on how much wire I installed.
So, to answer your question, how much wire is in a RV-7? Well, for me it's about 2,024 feet of wire. That's 497 individual wires, not including shield ground wires. The total wire weight is 17.3 lbm (this will change a little until I finish with all of the wiring as will the total wire length). The interesting thing is the heaviest sub system is the Landing/Nav/Strobe lights (2.36 lbm wire weight). It's not that the wires for this are all that beefy. It's that they are so long. The GTN 650 was next (1.95 lbm), mainly due to a lot of shielded wires and the RG-400 coax going out to the Archer wing tip antenna. The third heaviest sub system was the GNC 255A at 1.59 lbm (again, shielded wire and coax to the wing tip antenna). The fourth heaviest was the Auto Pilot (1.15 lbm). Again, a lot of small, really long wires. The fifth was the starter system (1.02 lbm). Not a surprise there given the large wires used for it. However, they are relatively short so that's why the starter is fifth on the list. My "gut" feel before running the numbers was that the starter system wiring would be the heaviest since the wires for it are huge. I was wrong however.
Once I get finished with this I plan to clean up my spreadsheet and post my results here on VAF. I see a lot of people talk about how much this or that adds to the weight of the aircraft. Lots of opinion without any numbers to back up their claims. I'll have actual data to back things up. Of course, any changes to this will affect the numbers but it should give people a good idea on how much wire weight they are adding to their planes.
Another thing that was interesting was that if you were to switch from a 14VDC system to 28VDC, you could reduce the wire size somewhat and save some weight. I ran the numbers for this, keeping AWG22 as the smallest wire size due to ease of use and robustness. The weight saved was about 3.5 lbm. Not a whole lot. Especially when you consider that you're going to have to use a 24VDC battery and would most likely want to add something so you had 12VDC for things like charging Ipads, etc. Those extra items you will need by switching to 28VDC quickly cut into your 3.5 lbm weight savings. For me, it wasn't worth the added complexity to go to 28VDC so I've got a 14VDC system.
Anyway, I hope this helps. Please let me know if you have any questions.
Jeff