Hi Casey. Nice that you're planning a trip to Thailand, and you give us some good leads in regard to the way you're thinking, but you leave out one very, very important detail--when are you planning to come? Let's assume that you are totally open as far as dates go, then, okay? I will also answer only from the perspective of the Andaman Sea side of the country. It should be noted that there is also diving in the Gulf of Thailand, and some of my colleagues who have insider knowledge from that area are better equipped to explain the possibilities over there.
First of all, in regard to "When?" our main liveaboard season is from November through April, and the main destination for these boats is the Similan Islands. There are a few boats going to other destinations both during the same season and during the months from May through October, but not too many.
Next, while it's not a strict requirement by any means, I do recommend AOW for diving from the liveaboards, primarily because the dives tend to be quite deep, there is a chance of currents, and there is night diving. With just 8 dives so far, you may feel a bit unprepared for the challenges of some of the dives from a liveaboard, though they aren't exactly "double black diamond" type dives and are manageable with the right sort of technique.
Traveling solo isn't typically a problem here in Thailand, though if you're an old fart, you might find the low-budget liveaboard boats too much overrun with backpackers and 20-somethings for good social interaction. Solo travelers do want to meet others with whom they have something in common, so I'd recommend a mid-priced boat for somebody like you. At any rate, our dives are done in groups with buddy pairs assigned from within the groups, so you will be placed in a group of divers led by a DM and you will have a buddy.
If you have lots of time, you might consider doing the AOW on daytrip boats before getting on a liveaboard for sheer enjoyment of diving from the liveaboard with no need to study, or you may do your AOW on board the boat itself. I like teaching the AOW on liveaboards, personally, since it gives me lots more dives to work with my students than if we just have the daytrips, but there are advantages and disadvantages to either option.
For landbased options, there are a number of places you can base yourself, including Phuket, Krabi, Phi Phi, Khao Lak, and Koh Lanta. Phuket offers the greatest variety of options and schedules.
Hope that helps a little!