The G&G G96 is pretty much the same thing as the Tanaka rifles, excluding the magazine.
Although I've never had any hands on experience with the G96, I have read upgrade guides because I though about doing this once.
Only problem is that it has the same crappy hop-up unit as the stock Tanaka rifles. You could upgrade to the VSR conversion hop-up though. To allow that to work, you would either have to buy a KJW bolt or Tanaka bolt because of the short air nozzle of the power bolt that can't be removed.
I would say that the KJW would cost less money to get going. I actually have a KJW that I want to sell. It has the Tanaka AICS stock and a G&G Heavy barrel (acts as a full length barrel spacer). I do not have a magazine though. I bought a G&G G96 magazine hoping that it would fit, but it doesn't (yet). I'm going to mod it to fit soon though. Even if I couldn't get the magazine to fit, then the power pack parts in it would still work. I would let this rifle go for a pretty cheap price if you're interested though.
Back on subject though, an HPA rig and a bucking are really the most beneficial upgrades for this rifle. After that, I would then say a barrel, then striker spring, and then G&G parts for the magazine.
Another good thing about the KJW is that it already accepts the VSR-10 buckings unlike the Tanaka and G96, which needs the $80 hop-up conversion unit.