What happens if i dont get a tune?

if they do their job you will probably run lean - if lean enough the ECU will pull timing and your idea to add performance will be negated... read up in the intake/exhaust section – there is quite a bit of info and I’ve posted my experience several times.

I just noticed you don’t show any breather mods in your sig ( besides Stillen intake)... maybe you should start with plenum spacer, get the exhaust where you want it, then consider HFC... you should have all your breather mods done before you tune - any one of them could affect your a/f.

Now, if decide to sell my car down the line, and take my mods off, do i have to get it all re-tuned?

short answer, yes... but it depends on what you use to tune.

most shops wanted hr worth of labor to do mine when i went but now i have to go back and get another hours worth to remove them cuz im gettin TT