Hi, Lance! Welcome to the forums.
Firstly, I'd like to point out that the current AI War prerelease,
2.001N, has a 3 hour trial limit rather than 2.0's 1 hour trial. Prereleases typically have a lot of new features and enhancements over the latest official release, but they can also be more buggy or unbalanced. Still, if you feel the need to try the game out more before making a purchase, feel free to give the prerelease a try. Just note that the prerelease also has expansion-related features that are in trial mode by default, but you can disable those in the expansion tab of the settings menu. More information is available in the 2.001N thread.
Also, I want to make it clear that Steam accepts AI War license keys purchased from any source, so users purchasing the game through the Arcen Games web site or even from other distribution services can still unlock it on Steam, free of charge (and similarly, users purchasing the game on Steam can use their key to unlock the non-Steam version available for download on our web site). The Steam version offers online leaderboards and achievements which are currently unique to it, while non-Steam versions only have offline versions of these features.
Multiplayer for AI War happens decently often. Looking around online, at threads on this forum, and at IRC, I feel like people who want to find a game to play typically do. I manage the IRC channel and see games happen there pretty often. Hopping in there while people are chatting and asking if someone's up for a game can often work out pretty well. Sometimes games are 4 people large, sometimes just 2 or 3 people. The reality is that the AI War playerbase, while pretty decently sized, isn't the biggest thing around, so finding massive games happening all the time isn't currently the case. It's steadily expanding, though, and promotions in particular help drive sales and activity a lot, so I wouldn't worry too much. I recommend IRC in particular as a way of finding games; I'd guess it has the best success rate. Feel free to drop by and see how much it's frequented, though I warn that its level of activity can be rather unpredictable. I try to be responsive anytime I'm not at school or sleeping, though. If you have an IRC client, I recommend just joining the channel and maybe joining conversation when it happens.
I've not seen any games happen from the official group on Steam, but there's another group (Avengance) that I've seen spawn some games. Neither seem to be particularly frequented at the moment, however; I think IRC may still be your best bet.
Regarding bonus ships, there is a limit of 8, but (to my knowledge) games never have more than 5 advanced research stations, so you won't hit that limit in any typical game. You'd have to be starting an atypical game with 4 or more homeworlds in order to run across it, and with that many homeworlds, your unit caps should make up for it. Too many ships is also energy-intensive, so supporting many more ship types with your economy would likely be difficult.
Not picking your favorite ship type could be advantageous, but then you don't get to use it in the early game, if you ever get it at all. It's a gamble.
I've not done too many multiplayer games, but I imagine things don't get too homogenous with everyone having access to similar ship mixes, particularly considering the large areas people have to cover in those sorts of games. Tactics are also a big part of how AI War plays out, so how the ships are used is important and will help differentiate similar armies. Unfortunately, my lack of significant multiplayer experience makes it so I don't know how roles work out in late game, but I don't see why you wouldn't be able to get the roles you've been playing so far work. Just keep in mind that the game scales in difficulty for multiple players, so you might be forced to take a more active role to take a particular planet or defend against a massive wave.
I hope this answers much of your questions. We're happy to respond more, if I didn't answer a question well enough or you're curious about anything else.
