hi there i am new on here but do a lot of car detailing semi professionally 3 or 4 cars per week to include full swirl removal etc just a few pointers.

please note i am not going to set myself up here as an expert with perfect knowledge of all aspects just that i have done lots of cars and i feel i am able to help fellow buftys.
i also am not here to sell my services or products but as i buy most of my products from the internet i can at least direct you to somewhere that can.

any way here i go

for a new person g3 is not the best thing to use as it is going to be very harsh it is used mainly to remove wet sanding marks on fresh paint after wet flatting and in the hands of professional body workers has been known to leave hologramming (almost like smears that seem to be 3 dimensional in the paint) which are caused by using too coarse a polish with high speeds of a rotary machine.

if you wish to give the vehicle a quick spruce up and leave yourself with a large margin for error buy an all in one polish like klasse all in one or carlack 68 or sonus swirl buster or sonus sfx 3 these can be applied by hand and will break down easier (by hand they are never gonna make a great finish) however using a machine they come in to their own

on the subject of porter cables they do cost a bit but are available for much less money if you shop around and are the finest dual action polisher for the money they are easy to use and you would have to be ham fisted to cock anything up with a porter and an all in one polish

you would be much worse than to buy a swirl buster pad and swirl buster polish with a porter cable machine as the swirl buster polisher has the ability to remove most of the defects and also has a large percentage of acrylic fillers within that fill in the swirls to make them much less visible (however it will not give 100% removal)

a simple product like this topped up with super resin polish or an acrylic sealer like klasse all in one will leave a really nice finish on light colour cars and with reds and dark colour cars a coat of wax will give more warmth to the finish (natties blue or red are good starters)
hope this helps
dave
ps i just bought another dual action polisher (udm) from the states for 59 pounds including shipping with a trasformer from screwfix it was a lot less than on ebay