I'm going to try not to go over board with this post...
An orbital buffer, such as the ones you find in local stores is only good for applying LSP (Last Step Products), such as a wax. It is not going to do any paint correction.
The Megs buffer you mention for $150 is a Dual Action (DA) buffer. It's safe in the hands of a novice and still won't damage your paint. It does require special foam pads with hook and loop backings. Megs is coming out with their G110v2 in mid December. This one is much better. A pad kit is going to run around $50 or you can pre-order the G110v2 for about $170 with a good Megs pad kit. This is a good price.
A rotary is another animal (a pad on a drill would be about the same thing). This _CAN_ damage the paint in the hands of a novice if you are not careful. You need to know how to keep the machine level and moving all of the time. This is not as easy as it sounds. A rotary will correct paint defects very quickly. This is why professionals use it... but they also use DAs all of the time.
There are a few polishes that you can buy locally to use with machines. Megs Ultimate Compound is the strongest consumer polish that Megs offers. It's very safe. A step down is ScratchX 2.0. ScratchX 2.0 can also be applied by hand and does a great job in removing scratches and micro-marring.
A LSP product should be applied at least every 3 months. After that and the product looses some of it's protection. Weather can reduce this time frame.
Liquid or can.... LSP functions the same.
If you want my opinion, I'd go with Megs NXT 2.0 sealant. If you have a dark color vehicle and/or want a little more pop to the paint, let the NXT cure for 24 hours and put a good carnuba wax over it. NXT 2.0 has a little polish and some good fillers in it. This would be a simple, one step process. Either that or a good cleaner/wax for a one step process.
Pick up some good microfiber towels. Locally, Target sells the Vroom ones that are pretty good. Use these to dry the vehicle and also remove the wax. Last I checked, they were on clearance.
I have a PC 7424 and about 10 assorted pads for it. I can't tell you how many polishes and waxes I've bought ('cause I'd have to kill you) but I can say they are like kites... you can't have too many.