OK, you mentioned you have a Sentra SE, and it likely doesn't have components in it (tweeters in the A-pillars). If you HAVE to HAVE components, you simply need to get the A-Pillar interior Bezels from a Sentra that had the higher model of stock stereo (these will have the tweeter pods, and should drop right in), which you can get from SER's/Spec-V's. These you can get from a scrap yard. You would simply put the woofers from the component set in the stock location in the doors, and re-use the OEM wires for them. Then you take your original pillar covers off and swap the ones with tweeters in. The tweeters will be on a small track-like bracket that simply screws into the A-Pillar, and the trim has the tweeter pod molded into it that fits over top (for tweeters 1" an smaller). You would just need to feed the wires from the tweeters under the pillar trim and through the dash. The crossovers for the component sets will fit inside the center of the dash under your stereo (mine are like this, and they are friggen huge...consult here: https://www.b15sentra.net/forums/showthread.php?t=191625
Now, if you feel you don't need to go to the time and expense for components, you can get some really nice sounding 6.5" coaxials to put in the doors alone, and then the same for the rear deck. Again, if you don't want to break the bank, run the fronts and rears off your HU (if it has an internal HPF and runs 20watts RMS or more per channel).
You won't go wrong with Pioneers, JVC DRVN or Arsenal, Kenwood, JBL, Infinity, or Power Acoustik. My parents have the JVC DRVN 6x8's in all 4 doors of ther 2006 F150 Supercrew, and they ar being driven off a JVC double DIN touchscreen HU and sound really good. I have had Power Acoustik 6x8's in my Focus that sounded fantastic, also just driven off the HU.
For Bass, I would go with a good quality 8-10" (only 1), loaded into a ported box, as you said that you crank your bass all the way, so the ported may yield more SPL for your tastes (I think sealed would work well too, just need a bigger amp, and a box that is the specs your sub calls for). You could use a Single 10" and would want to drive it with more than 150 watts RMS. Things are different now than 10 or more years ago. You don't need close to 1KW to drive modern subs loud like in the past.
You could consult the installation that is in my car in the above quoted thread, as it may be a lot like what you are doing with your own car.
Let us know if you need more advice!