Just get some 9 Wire Stinger Wire. For the amount of watts you are running you don't need to run new speaker wire. It incorporates all 8 speaker wires plus a remote turn on wire. You run it from the amplifier to the aftermarket wiring harness. Instead of attaching the head unit speaker wires to that harness you connect the 9 wire speaker wires to the aftermarket harness instead and it utilizes the stock OEM wiring. Most wiring these days can handle 100 watts easily. I have the model before that of that amplifier installed in my 2003 Ford Explorer a GM-D8604. Same amplifier just new casing is all.
If you are just going to do a 4 channel with and those speakers then find a 4 gauge OFC kit as you will also need 4 channel rca's. Personally I just switched to these rca's from Sky High 4 channel for 28 bucks and they are OFC as well. From there you just need a ANL fuse at the battery and then a distribution block in back if you ever decide to upgrade to a subwoofer setup. If you are ever going to upgrade to a subwoofer in the back then 1/0 OFC power and ground. But whatever you find for a kit get OFC for the wire. And nice thing with that 9 Wire Stinger Wire it has the remote turn on built in so no need to run that separately.
9 Wire speaker Wire
https://www.amazon.com/dp/B01LXI9LBI/?tag=caraudiocom-20
4 channel OFC rca's
NVX, Sky High Car Audio, KnuKonceptz, Stinger and a few others all make OFC kits. NVX has a complete OFC kit with 4 channel rca's on
Sonicelectronix for 109.99 then you would just need that 9 Wire Stinger Wire. Never want to cheap out on power, ground and rca's.