Help/Guidance needed for Audio Upgrade under $500

[FA20D]

Hi Everyone,

I recently just purchased a 2014 Scion FR-S with 45K miles - I have 8 speakers in the car.

I want to upgrade the audio in this car as its pretty horrible. My budget is around $500 max, the car already has a Pioneer NEX with wired CarPlay. I do plan on upgrading this down the road. I also plan on adding sound deadening with a combination of dynamat and MVL. For context I listen to a wide variety of music, but mainly listen to Jazz, Pop, and Synthwave currently. I'm looking for a clean clear soundstage with some dynamic range. I don’t need a ton of base, but like to have a warm tone in my audio.

From all of the research I've done on this forum/reddit/YouTube, I have a decent idea on what to do but im not entirely sure how to execute it.

Plan:

1. I was going to switch out the door speakers and front tweeters for Focal IS Toy 165's - these are supposedly plug n play with the factory harness and mounting. But now I'm thinking I should get a 3-way component speaker set and just use metra adapters. If I did this, would I have to wire into a crossover for the tweeter and the 3.5 in the dash? Also are there good mount adapters for the door speakers or should I just cut out the existing speakers and fabricate my own mount using those?

2. Get a 4ch amp and use a wiring harness adapter from metra to keep the factory wiring. I'm trying to avoid having to disassemble everything. I've seen some people use the Alpine KTP-445U re-wiring a Metra Adapter that @RandomHero documented here https://www.ft86club.com/forums/showthread.php?t=42239. If I don't use the alpine, I was planning on running a power wire from the battery.

3. Get a compact powered sub to run either behind the rear seats deck or underneath the drivers side seat. Wire this into the aftermarket amp. This doesn't need to happen immediately, probably a later upgrade.

With this setup I'm not sure how the rear speakers factor in, or if I should just remove them altogether?

Would this work, am I missing something obvious? Does anyone have different speakers recommendations? Also any amp or sub recommendations?

Lastly I don’t want to spend $1500 on the OEM Audio + system.

Any help would be greatly appreciated!