Hi Gary, I don't see why you wouldn't be able to do the lower arms yourself. The back section of the exhaust is suspended on 3 rubbers, so just pry them off and let the exhaust drop, you might need to use a bungee cord or something to help support it but you only need to drop it enough to give access to the rear bolts. Seeing as you have done the upper arms and bushes there is no reason why you couldn't do the bottom ones IMHO.
As for the gearbox and a transmission fluid change I would say it is possible BUT if you don't have a lift it would be a bit of a challenge. I think if I didn't have a lift I would be speaking to a local Land Rover specialist or a transmission specialist as we know, the gearbox is fussy, you must use the right spec fluid and it has to be filled in a particular way.
Best of luck with it.