Cheap and performance parts don't go together. Where you can buy standard discs for around £40, performance discs are well over £100 pair. Even then some are better than others. Mintex do a good middle of the road part. And buypartsby also sell performance discs ... remember they are a motor factors, so don'tmake anything ... just resell it.
Standard discs with DS2500/Performance pads have been a favourite on here for some time. Also replace the brake fluid with Super DOT 4 or 5.1 (eg Castrol Response).
When you say you need new suspension ... what bits? Changing to GTA items will mean new discs/calipers/etc. They aren't the same as the V6 items ... they're closer to TS units.
You'll probably be better off making sure all the bushes and joints are ok, which invariably means new arms, wishbones, droplinks, etc. Front and rear.
Then, and only then, invest in a good set of shocks and lowered springs. Those sportpack units will be slightly lowered, but are they for a V6? The TS springs might be too soft ... then there is the question of how old are they as the shocks may be past their best.
When Alfa released the 156, the Sportpacks were fitted with Eibach springs and Bilstein shocks. Some stick with this mix or go to Koni adjustables, etc. A lot is personal preference and more to do with the depth of your pockets ....
Run a few searches on the site to see what the others think/have already posted.