Welcome to Autopia!! Was going to respond to your post in the introduction section, but never got to it.
My point of view is from someone relatively new to machine polishing as I've only been using a polisher for a little over a year, but have had excellent results with very few problems.
IMO the Griots Garage 6" polisher is the best choice for those of us just doing our own (and perhaps a friend's or relative's on occasion) cars. It is the most powerful of the "standard" reasonably priced polishers and believe me you will appreciate the torque once you get into this. And, it has a lifetime warranty and Griots customer service is excellent. That being said it will cost you a little more than the HD kit as you need to replace the backing plate with a 5" ($15) backing plate so you can use 5.5" pads. While the GG6 can handle the 6.5" pads the 5.5" are preferred as you will get better performance and they are less expensive. If cost is an issue the HD Kit is great as it comes with everything you'll need to get started (but you'll need more pads)
Without knowing the condition of your paint it's hard to make firm recommendations regarding products to use--if you can post some pictures it would help.
HD polishes are are very user/beginner friendly--very long working times, little to no dust and very easy to remove as they don't leave heavy oils behind. UNO might be a good starting point as it is medium cut and finishes down very well, but you can always finish up with HD Speed to really make the paint shine. Or if your paint needs more correction you could use HD Cut then follow up with HD Polish or Speed. As Accumulator suggested HD Speed is a great product for your first attempt at machine polishing and for an all in one has a good deal of cut--I was able to correct light wash marring with HD Speed/orange pad on hard VW paint my first time machine polishing with excellent results. MOST Cut--HD Cut > HD Polish > HD Speed--Least Cut finer finishing.
For pads I'd recommend at least 4 orange, 4 green, 3 black and a couple of red (for wax or sealant application) HD or Buff & Shine pads (they are the same)--they are flat pads (no dimples) with recessed Velcro that IMO offers an extra measure of safety when working around protruding objects. Many beginner problems come from trying to do an entire car with one or two pads. MOST Cut--Orange > Green > Black > Least Cut Finer finishing--red has no cut. You need the various pads on hand as you won't know exactly what you need until you do your test spot.
Microfiber Pads are highly recommended by many, but I feel it makes things more difficult in the beginning as they require slightly different technique--I plan to add them later if the need arrises.
For cleaning pads on the fly use a denture brush (from the $ store) and a MF towel. For washing pads after polishing I use Dawn and Dawn Power Dissolver for tougher cleaning.
Here is some information and videos that may help (just don't use the pad priming shown with HD products)
The Definitive How-To Article for Removing Swirls, Scratches and Water Spots Using a Porter Cable 7424XP, G110v2 or Griot's Garage Polisher - Auto Geek Online Auto Detailing Forum
Cleaning your pad on the fly--
How to clean your foam pad on the fly - Auto Geek Online Auto Detailing Forum
I think HD Poxy would look great on yellow, but would require application every 3-4 months in my experience. As mentioned if you're only doing it twice a year you might want to go with a pure sealant like DG105 or durable hybrid like Collinite 845 or 476 which tend to last longer than many other products. Or you can put down a coat of DG105 then top it with Poxy so if you don't get a chance to reapply in 3 months you'd still have protection remaining on the paint.
Hope this info helps, but I'm sure it will generate more questions so just ask away.
) so the Speed/green combo will very likely not be quite aggressive enough to really clear everything up. It would, however, be a great way to get into the whole machine polishing thing, with zero chance of anything going really haywire.