Yep, Carlsson body kit. Nice snag!!
For the suspension, you have a few options. I would recommend the SAS 9Swedish Auto Specialists) sway bar kit which is thicker than stock and really sharpens up steering and improves cornering stability. You could also go with Bilstein struts and shocks for a stiffer ride. If you want to lower the car, there are a number of spring options including Intrax and H&R. Every 9000 I've lowered has had slight rubbing issues with any wheels wider than 7", so be mindful that a low car may limit your wheel options.
As far as I know, all 9000 turbo brake calipers and rotors were the same '88-'98. Those years had ABS, so I'm not which components would be compatible of if they'd really be an upgrade at all. I know "big brake kits" are available for the later 9000s, but I do not know about the 1986-1987s. Maybe someone else on here does.
You could go with EBC Red Stuff brake pads for more braking power using your current setup. I have drilled or slotted rotors on a few of my cars and I like them, but others say they're just for looks. My 9000 is extremely fast and I've always found the stock brakes with good pads are more than adequate. My recommendation is to get some good brake pads and sticky tires. A car can only stop as quickly as its tires will allow.
1987 900 turbo convertible
1993 900 Commemorative Edition #50
1995 9000 Aero - Stage 3
1996 900 troll
2002 9-3 Viggen vert - Stage 4
2004 9-5 Aero Wagon