Ready to upgrade JBL speakers. Questions

I've read through almost all of the threads regarding upgrading the JBL system and want to make sure I'm making the right decisions.

1. The JBL amp is 45x4 watts at 2ohms, right? Is this RMS or peak rating? I assume that I'll need to find efficient 4ohm speakers or find 2ohm speakers to match?

2. Since the front speaker crossovers are at the amp, will there be an issue with not using the crossovers from the new speakers? I thought each speaker had different crossovers for a reason.

3. If #2 is a problem, I'd like to buy an amp for the new speakers, but I don't want to lose any functionality on the steering wheel (volume control, bluetooth, etc). Does this mean that I should use the rear speaker outputs to high level input of the amp, since the rear speaker outputs are full-range? That would allow me to use the new speakers' crossovers.

4. If I want to keep bluetooth, does that mean I need to use the JBL amp's front channels?

5. For #3, I should get a 4 channel amp to power the new front speakers and stock rear speakers, right? Is it worth it to move the stock front speakers to the rear?

6. For a sub, I don't want to take up any trunk space so I've decided to put it either under the passenger seat or in the rear compartment above the spare tire. I'm thinking about the Boss BASS600 is the best available. Which location is best?

I appreciate any responses and sorry for having so many questions!