hi jason. i originally lived in banbury, oxfordshire so not far away.
as stated, i would start with 40wt oil in the shocks and see how that goes.
i would use 15k in the diff.
you may find as the baja has been sat for a few years that the carb might be cloged and gummed up as this happened to mine after i left it for a year lol so a new carb or strip and clean of your old one might be on the cards.
as for radio gear you will always get different opinions. i run a sanwa radio now but have ran the flysky in the past and it was ok to start with.
you will need a 3 channel radio at least if you want to run a kill switch so you can use the 3rd channel for the kill switch.
there are many different kill switches out there so have a search. switchblade,killerbee ect.
as for upgrades i would recommend the following
if you are going back to stock gearing, i would be looking into the vertigo clutch bell as the bolts can snap easily in the stock clutch bell.
hostile spur gear or a steel spur gear as a stripped gear can end play pretty quickly.
the front steering rods are pretty weak in stock form but will be ok to start with.
basically i tend to upgrade as i break stuff as everyone drives differently and my break things that others wont lol.
just have fun and upgrade along the way.