not sure such a thing as uprated suspension arms exist. just get some good pattern parts and fit them properly. the bottom arms should last a good few years anyway, dependant upon how they're driven and what sort of roads they're driven on but the bottom arms are not that bad. its usually top arms that suffer and that is purely because people are dumb when they fit them and leave them way way too dry.
as for restrictive EGR gasget, don't waste your time, it will only block the dam thing up quicker and cause more errors. just get the whole care remapped and the EGR written out properly, more power better economy and job done properly.
as for brakes, good luck trying to fit GTA 305s. there is no way to manage this without the GTA uprights as the mounting holes on the uprights for standard cars are different to that of the GTA. a better approach maybe to get the calipers off of a 166 and have a bracket made to fit these. the hole spacing on the 166 calipers is greater still than that of the GTA spacing so allows room for a bracket that the GTA calipers do not.
the only GTA option you have is the 330mm radial mount calipers, which you will again need some brackets making up to acconut for the spacing on the uprights. furthermore on the 330s you will need to make sure you have the GTA teledial alloy wheels, 17s or greater, as the 17 inch multi-spoke alloy wheels from the GTA will not acomodate the calipers due to the mounting bolts on the radius. you could either space them or try really shallow bolts, but it aint ideal.
1999 156 1.8TS Sport Pack 3
2001 166 3.0 V6 24V Super
2003 156 GTA 3.2 V6 24V
2005 156 1.9 JTDM-Jet Sport
2008 159 1.9 JTDM Lusso
1997 GTV 2.0TS Lusso
2001 147 1.6TS Lusso