If you lost an arm, work towards getting a cybernetic replacement with +1 agility.
Special Modifications allows you to build it for half the price you buy a new one for.
You'll need a mechanically inclined party member though.
The Hutts replaced it for free since we all ended up becoming slaves and had to participate in some gladiator-style battles. The GM is including a recovery period for me to get used to the new hand before I can gain the benefits.
Caveat: we have a house rule that allows us to purchase characteristic upgrades after character creation.
Not tryna rain on your parade, but do not do this.
You will obliterate any chance of game balance.
This isn't a system where the heroes are maxed out every stat, and allowing this will essentially be running your game in Cheat Mode.
If you listen to no other advice, listen to this.
This isn't just a standard group, as this is a two-group game and there will be pvp going on so no one is getting something that the other isn't. I do understand what you're saying, but this was the GM's call and we have already gotten into the game so I don't seeing that change.
Also to answer a question, generally defense from different sources do not stack. There are some cases such as Improved Armor master where it is implied that the defense you get from the armor is increased.
For example, melee Defense +2 from a souped up lightsaber is not meant to stack with +2 defense on a shield or on armor or from cover.
(also "guy" can be gender neutral for at least 30 years where I come from, lol)
What I was mainly talking about was whether two guard shotos would give me increased defense, as I would go with another weapon otherwise. I'm going to guess they don't, but it doesn't hurt to ask.