definately go for the kit, the plastic steering arms are rubbish on all the rtr`s
as for upgrades, more steering lock, look on ebay at seller rcmart/dinball he does 3 racing steering knuckles/c hubs/cvd driveshafts this makes tons of difference when on full lock (turns much tighter)
depends on if you want to run in water but i use a traxxas xl5 esc in mine which is ok but if you want something with drag brakes go for a rooster or tekin fxr (crawler one)
steering servo can be done a few ways too, if going to be used in water, i use the tower pro mg996 servos, about £6 each from hong kong, mines been in for over a year and been under water too with no problems or go for a savox 0251 or 1256tg both will give buckets of turning power (the tower pro ones do too)
are you running or plan running it on lipo`s? if yes dont bother with the battery tray mod if running nimh`s then yes move the battery tray up front.
go to a kwik fit or similar, get some of the stick on alloy wheel balance weights (bout 3 strips for each front wheel and 3 strips for both rears) they will look at you funny but its a lot cheaper than buying them off ebay.
use some motor grub screws to fill the holes in the axle tops too to stop water and dirt getting in there.
have loads of fun, great truck which no other company will beat for now at least.........
if you need any more help, give me a shout, only too happy to help, gaz.