phatrs- Welcome to Autopia!
While I realize that you won`t like this response, IMO you oughta be doing far more research before trying to do this stuff. Not watching YouTubes, but rather learning/understanding the concepts/processes/physics involved so you understand this stuff inside-and-out before you start. It`s pretty simple stuff and once you understand it things oughta go very smoothly right from the jump. Trying to do it without a complete understanding will be much harder IMO.
At least learn what types of pads are used for what kinds of work, and what the major Product Categories are all about.
But OK, OK..few people go about this stuff the way I would, so I`ll just shut up about all that
Do you have proper Inspection Lighting? That is *absolutely critical*.
Now, to actually address your Qs:
I also have Meguiars Ultimate Compound. Is that considered a one-step polish?
No, it`s a Compound. Compounds are more aggressive than Polishes and require a follow-up (generally with a Polish) to remove the micromarring that Compounds leave behind when the "sand down" the scratches/swirls.
A One-Step Polish will not be as aggressive as a Compound, so it won`t remove deeper marring (at least not as quickly), but it`ll leave a nicer finish and just "making things better but not perfect" is a good initial goal when you`re starting out.
There are All-In-One products that are *real* One-Step products since they combine a mild Polish with Paint Cleaners and some kind of (generally short-lived) protection. These are typically *VERY* user-friendly and can be a great way to start.
1. After putting 4 “pea” sized squirts of a medium compound on the pad and starting slowly before moving up to about 5/6 speed, the product is flinging quite a bit.
While I like high speeds like that, many (most?) others would limit it to about "4". You don`t want the product to dry out too fast.
Also, work *SMALL* areas at a time until you`re dialed-in; I would not (and DON`T) do the "two-foot square" size area that many advocate, way too big for me in most situations (and I`ve been doing this stuff since forever).
Is that "four pea-sized.." approach the proper method to prime using the product in question? I don`t know that product, but different products can call for very different priming approaches.
THERE SHOULD NEVER BE ANY "FLINGING" OF PRODUCT. Not under any circumstances...something`s really haywire there, wonder what...
I assume you`re keeping the pad in relatively firm contact with the vehicle, and keeping it pretty flat.
2. The polish was really hard to get off after, like it was really dry. I tried doing less passes before wiping it off and it was much easier but then I seemed to make no impact on the swirl marks.
You must`ve overworked the product and/or let it dry before buffing it off. Virtually all Compounds/Polishes...*BUT NOT AIOs* are buffed off while still a little "wet", before they dry.
Doing significant correction on hard clear can take a *LONG* time! Even with really aggressive products (and I doubt the stuff you used is like that).
It can *really* take forever when you have to stop frequently to buff off the product, strip the Polishing Oils (I find IPA terrible for this compared to dedicated products made for the job), inspect your progress (with that perfect Inspection Lighting

), clean the pad (or get out a new one), reprime the pad with fresh product, and get back to work. Just the way it is.
Upping the aggressiveness (e.g., using a Microfiber Cutting Disk instead of a foam pad, using a very aggressive Compound like Meguiar`s M101) can speed things up, but will also take off more clear faster and make the chance of a serious "oops!" more likely, so it`s always a trade-off.
I`ll repeat the "aim for `better` instead of perfect".
I`d work a very small area until you get it the way you want it...or until you either think "Oh man, enough already!" or until you start to think you`ve taken off enough clear (you can`t take off much without precipitating failure). Pick some area that`s 1) representative of the vehicle`s overall condition marring-wise, and 2) pretty easy to work on/inspect, and try to get that one area "good enough" whatever that means to you. That`ll give you a better idea of what`s going on and how that matches up with what you want.
Again, I realize my response is quite probably not what you`re after, but I do hope that something in the above is useful. It`s entirely possible for somebody to research this stuff and then pick up a polisher and do fine *the very first time*..as long as they define "doing fine" in a realistic manner. Don`t expect to get the exact same results as somebody who`s done this for a few decades, at least not at first. Remember that your polisher is merely "a fast hand that doesn`t get fatigued", it`s just moving the pad/product across the surface the same way you`d do it by hand.