I have the Kartboy endlinks on Whiteline sway bars and they are nice! Here's what I would recommend:
- CNT Downpipe: save yourself a couple hundred dollars (hit up m sprank for great prices)
- Grimmspeed 3" DP adapter
- Infamous eTune
- Rallitek Springs: probably the most conservative drop you'll find
- Turbo: BNR EVO 16G if you're looking to do a 'small' upgrade
You shouldn't have any emissions issues with an aftermarket UP, but as you already mentioned you likely will with a catless DP.
Hope this helps