You're already getting good advice, lemme jump in here with some of the results of trial and error and spending a couple of years buying stuff that I wish I would have started with in the first place.
The GG DA is a good choice. The GG, PCXP, Meg's 110v2, Flex etc are all good machines. Only the GG has a lifetime warranty. If you sign up for their newsletter on the GG Web site they sometimes send you a welcome message with a limited time discount offer.
I started with 6.5" LC pads. Picked up a backing plate and 4" pads for spot correction and tight spots later. I ended up with pads of every color in the rainbow and found I was only using a few colors regularly. After trying the 5.5" pads I discovered they were easier for me to work with, corrected better and were still large enough to cover wide open spaces. If I were always working on a 70's Lincoln with an acre of sheet metal on the hood, trunk and roof I'd probably go with larger pads. But I found I really liked the 5.5s much better.
If you're just starting out and only working on your personal vehicles anything that can do double duty saves money. The cyan HydroTech will take out any defect you're likely to run into depoendent on aggressiveness of the polish. The tangerine HydroTech corrects milder defects well and finishes nice... very nice combo of attributes. I'd recommend starting with a couple of each in both 5.5 and 4" sizes along with appropriate backing plates. If you're going to apply an LSP with a DA you'll want to pick up at least 1 blue or red pad as well. I prefer flats over CCS.
As for polishes, Meg's 105/205 combo is tough to beat for versatility. There's a bit of a learning curve but if you're just starting out you don't have to unlearn what you've been doing with diminishing abrasives. An added plus is they're both available in 8 oz sizes.
You can chase the carrot continually and spend money on equipment and supplies but IMO, the above is a good place to start.
TL