Battle Dress uses a "Slot" which is roughly equivilent to a pistol in size. A vehicle weapon of up to 3 Spaces can be mounted on a Battle Dress - the exact number dictates where the weapon can be mounted - 1 Space on the arms, 2 on the shoulders (presumably an up-and-over mount?) and 3 on the back (either indirect or an up-and-over mount for sure). Small arms can be mounted internally to the suit.
As for sizes, shipped, a suit ranges from 0.05 to 0.25 dtons in size, while worn, a suit will fill 1 entire Space in a vehicle at least, an Ultra-Heavy will fill 3 (+ heavy weapons storage).
One system I forgot to mention is the new Stealth system - where Stealth, comms and similar technology are all compared according to TLs... a higher TL system will find it easier to hack into or defeat a lower TL system, meaning that you might want, for example, to fudge the TLs a bit when designing, so you have (for example) a TL9 suit that a merc company can keep running easily, but with TL15 sensors, computers and ECM and keep plenty of spares for those more advanced systems - or suffer the consequences of an inferior suite of electronics in combat.
Incidently, one little note I found funny - is where it mentions that suits can be controlled by an Expert program in the case of the operator being incapacitated... I just had an image of a sedated recruit, stuffed into the suit and waking up to find himself just landing after being shoved out of the back of a transport plane... thanks to the Expert programs that handled the grav-drop and then administered the stimulant through the built-in medical systems.
Oh and I forgot to mention - electronic controllers are are also covered in the book - it was a relatively late addition, but both vehicles and suits can be given AI or Drone controllers (or, even a cyborg brain in a suit). So if you wanted to recreate the Battle Droids from the SW films or ED209 from Robocop, you can.
