No problem
Personally I just use the 4° toe-in brace without any special hubs (using the B44 hubs which don't wear out as fast though).
Caster is something weird I think, 30° is so much more easy to drive and gives you a car easier to predict in the corners, especially when traction levels can vary a lot in one corner. I once partially f***ed up a National using 25° and 2,5° toe-in on a high grip track, which makes the car lose its balance entirely. I'm using 30° all the time now, just great for this car.
The Ghea front bulkhead is something I use too, the main reason being the crappy AE quality, STD bulkhead just wear out too fast. The weight this bulkhead adds isn't a problem though, just leave it to that.
The weight of my car is indeed around 1650gr, but varies a lot. I'm using the Vampire 4400mAh packs, which are around 250gr. For very low grip tracks I add 2 plates of 50gr under each Li-Po half, so 200gr total. This makes the car weigh around 25-50gr heavier than a conventional Ni-MH set-up.
Very good advice is to test this on every track you race on. Here we have 2 astroturf tracks: the famous Kampenhout, which is high traction with dust on it in the afternoon, and Arendonk, very high grip. With both being the same surface, you'd think weight set-up would be the same, but it isn't. I'm using 150gr or more of lead in Kampenhout, in Arendonk barely 100. While barely feeling this in other cars, this made an enormous difference for me on the S2. The plates I put under the battery packs are 50gr each, but I made a weight of about 50gr (consists of 2 plates of lead taped together) which fits nicely in between the battery halfs. This way you have the option to run something in between 100-200gr. Just make some weights of 25 and 50gr.
Concerning inserts: if you want a bit more side bit grip, try new Losi inserts which are included in Ifmar Studs, Big Shots etc. For increased forward traction you could use a used Losi insert, which is considerably softer.
Any questions, just ask
Btw: I have a planted astroturf set-up for very high grip, any need to post it?
Btw²: big kudos to Elvo!