Good to have you aboard WASP20
A BUNCH of SP20s in various stages of mods from stock ever upward at the Xmas DOO cruise today, there will be pics up soon, check the cruise page out.
Can't speak for Bora with his feature car, but mine is lowered 40mm on Kings springs (apart from a whole lot of suspension/chassis mods). Should set you back around $450 fitted, mebbe a bit less.
Cat-back exhaust will cause you no warranty dramas and gives a lot better throttle response.
Warranty is no real biggie until you get real serious, they just don't guarantee what you replace and there are some carry on effects.
So engine internals, gearbox etc go out of warranty if you play turbo for instance.
But stuff above should give no real dramas. Shocks would be affected by springs I guess but they are OK shocks and when they go off after 50k or so with low springs you just upgrade them.
Hope that helps.