OK, I'm a newbie and I'm sure not on the level of many of the folks here but I have a couple basic questions.

On a tight budget so I made do with an

Alpine CDE 102 head unit (18 watts)
Infinity Kappa 692.9i 6x9 speakers in back (110 watts)
Infinity Reference 6022si 6-1/2" speakers in the door (50 watts)

Both pairs of Infinities are technically 2 ohm but with the speaker wire function as 4 ohm speakers.

I knew I'd eventually want to upgrade to an external amp and originally thought of the Alpine KTP 445 (45 watts). I'm now looking at a Rockford Fosgate P400-4 (50 watts but they often are actually higher in actuality).

My questions:

1) If the amp rates at 75 watts or so (or more?), will this harm the 50 watt Infinities? I don't play my music TOO loudly and only for around 1 hour at a time on commutes.

The 6022si's were the cheapest 6.5" speakers I could afford that would handle 50 watts. I wanted something that could handle 100 watts like the back speakers but could not afford this. Should I match these eventually? Will the RF P400-4 make good use of the 110 watt 6x9's?

2) What is the best way to add a subwoofer setup later on? The RF P400-4 can run in 2 or 4 channels. The Alpine only has 2 sets of preamp outputs in back. Should I keep all 4 speakers and use the P400-4 to power them, then rig another amp for a sub? I imagine Y-adapters would make this possible?

Thanks for any advice!