There's so much you could do, it's hard to know where to draw a line...
The engine and gearbox mounts will have to come off anyway, so it's worth replacing them if you haven't already. Even just new OEM mounts will make a massive difference if your current mounts are a few years old.
As Budgie suggested, the rack bushes would be worth doing, too. They can be a bit awkward to change because access is so limited, but with the gearbox out of the way, it's going to take no time at all.
If you're planning to remove the gearbox by dropping the subframe, I'd definitely replace the ARB bushes. They're a real PITA when on the car, but with the subframe off, they can be done in literally 5-10 minutes.