Hmm.... you can easily just put in dsp sound processor to upgrade ur correct sound.

Don’t bother with amp if your not going to change ur stock speakers. stock speakers won’t be able to handle it.
Yes audison bit 10 about 1700. Tuning and cabling maybe add another 300-500 depending on cable quality and length.
Also different tuner got different style. Like some tuners likes punchy music with a lot of bass but without an amp ure also limited.
But dsp will be the easiest upgrade at the moment for u and see if u like it and can always change the rest later.