Hi, and welcome to FFXIV!
First, there's no real need to "stick to a class" in this game - in fact, leveling alt classes and alt jobs will help you perform the others better, because you'll be able to understand what the various roles need from one another. And especially if you're enjoying them all, there really isn't a good reason not to keep going with them.
Regarding hotbars, that is definitely a problem this game has. Most jobs now have upwards of 25 actions, and you'll need quick access to all of them in an endgame setting (some have more, a few have less). Especially coming from WoW, where they just went through an effort at simplifying classes andcutting unused abilitiesarbitrarily butchering classes, it can be shocking to find a situation where you will fill up two 12-slot action bars and still not have enough room.
There are a couple of ways around this.
First, concerning macros, most people will advise against putting your rotations and combos on macros, and a subset of those will argue against putting multiple actions on a macro at all (unless it's something done pre-pull like Swiftcast + Stoneskin II, or Grit + Darkside). The reasoning for this is that the abilities all have independent uses, and you'll want to have them all readily available for when you need them, without having to first use an ability, or dig through a series of other abilities on a macro. Announcing abilities that require interaction is also handy; I've had a few healers thank me for announcing Divine Veil and Convalescence in macros, but in general, I don't keep multiple abilities on a single button if I can get away with it.
This leads us to the original problem: too many abilities, not enough keybinds.
As many have said, one option is to use a controller, as this will give you easy access to 32 abilities (and they're looking for ways to expand it to 48 and 64). This is accomplished primarily by switching between hotbars, which the 2.5s GCD enables pretty easily. You need to do some configuration tweaks to optimize it, but everyone I've known who plays it that way has sworn by it.
If you prefer a keyboard and mouse, though, the first thing to note is that action bars 1-3 are class- and job-specific, meaning that if you change jobs/classes, those action bars will change to how you'd configured them for that class/job. This gives you 36 slots that you can swap between for each job, which will help ease your keybinds slightly. The trick of using this is giving yourself easy access to all these action slots, and there are three ways I've seen it done:
- Hotbar Swapping - Similar to using a controller, this lets you rotate in your hotbars to your main hotbar as needed, so your keybinds are maintained, and you don't need to use any more modifiers. If you know your class/job, know how your hotbars are set up, and get comfortable, this is probably the most efficient way to access your bevy of abilities.
- Modifier Keybinds - If you use the default configuration for keybinds, hotbar 1 will be bound to your number row: 1-9 + 0, -, =. What many people do is assign a modifier to this sequence (or whatever sequence they have) for hotbars 2 and 3. For example, holding Shift will pick from hotbar 2, and holding Alt will pull from hotbar 3. This gives you a way to easily access all of your abilities, and shows them all on your screen, but has the downside of requiring more of your fingers and attention to accomplish.
- Big Abilities on Mouse - I've seen this UI increasingly commonly in tutorial videos on YouTube, and have adopted it myself. This method uses hotbars 1 and 2 in either of the above methods, but enlarges hotbar 3 and places it nearer the center of the UI than the other two. Users then put rarely-used, situational abilities on this hotbar, so they are close to the action, and easy to access via mouse click. I keep things like Hallowed Ground, Provoke, and my tank stances on this hotbar, so I have them close at hand, but am not at risk of accidentally using them before I mean to.
All in all, the UI has some pretty powerful tools to help players access their abilities with ease. It does seem a little daunting at first, but it can be extremely effective when used well. Best of luck with your setup!