Rule of thumb is to have your amp within 10% of the rms of your speakers or having your amp less powerful then your speakers. This is so that you dont blow the speakers. For subs...this is hardly ever followed though, but it is a good practice.
Using 2 amps is perfectly acceptable. One amp for the speakers & 1 for the sub...or even 2 amps for the subs depending on setup & car.
Options really are limitless and come down to how much wiring you want to do. On some cars wiring is easy (Jeep wranglers for instance). Others...like the 986, it's a royal pain. I always prefer to run all new wires to everything using better gauge wires. On these cars though the ends just dont justify the means. Meaning running new speaker wires to the doors just isn't worth it. Running wire for the rear speaker tray is easy though and I always use a disconnect setup there so that it can be removed. On the cheap end you can just use spade connectors...which I dont recommend or get any 4/6 wire disconnect setup like these:
https://www.amazon.com/Waterproof-Electrical-Connector-Terminals-Assortment/dp/B0912NWT6H
I will typically run 6 shielded twisted wire rca cables along with a turn on wire from the head unit to the amp(s). The amp(s) I will install in the front trunk. I'll mount them in the same spot as the OEM amp and/or where the CD charger went. Getting some sheet metal from any hardware store you can bend/cut a bracket to mount it.
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