trev if you are not too confident with the g3 you could start with something a bit easier.
first off what machine are you going to use to do this mate

second poorboys ssr2.5 will remove most of the scratches you describe but will need working hard enough to do the job ie not by hand

third pick cutting pad to do with first to remove most of the scratches then you need to really use 2 further stages to get the scratches removed and give a finer finish like sand paper you ideally would stick to ssr 2.5 then 2 then 1 then an all in one polish followed by acrylic then a wax if you really want too

i would not reccomend going from g3 to lsp (last stage product) as the finish will not really be good enough and it will show

dave
you have pm