Jeep XJ audio upgrade

So I need some opinions and suggestions. I have an 01 Jeep Cherokee that I'm upgrading the sound system. Nothing crazy, just looking for something I can enjoy while getting from A to B and maybe cranking it up once in a while for when in the mood. The jeep came with a Kenwood KDC-352U HU, and stock speakers. I changed the speakers last year to 4 Polk DB652 6.5 coaxial, sounded better but not very good at high volume. So last week, after looking here at articles and post, I decided to put in my old Rockford Punch 800.4 amp. Bought the RFK4D amp kit and installed it, plus routed new speaker wires. Huge difference but now I'm lacking bass. I have 2 12" RF Punch HX2 RFD2212 that I had paired with my amp in the early 00's. So my questions are as follows

1- The volume on the HU is very low until it goes to 22 (35 max), how can I get it to go up gradually from 0 to 35?

2- I tuned it the best I could, amp crossover set @ 85 and my gains are at maybe 45 with bass punch boost at 0. will it be ok to crank it to 30+ without blowing a speaker?

3- Looking to buy and amp so I can hook up my 2 12's, so should I leave the RF P800.4 amp on the speakers or place it for the sub?

Thanks 

Amp https://www.crutchfield.com/S-erpbwxMyKyk/p_575G18004/Rockford-Fosgate-Punch-800-4.html

Subs https://www.crutchfield.com/p_575RFD2212/Rockford-Fosgate-Punch-HX2-RFD2212.html

HU https://www.crutchfield.com/p_113KDC352U/Kenwood-KDC-352U.html

Speakers https://www.crutchfield.com/p_107DB652/Polk-Audio-DB-652.html