The main draw of the game from a mechanical standpoint is that your class is tied to your mainhand weapon. Throughout the game you can pick up various quests from the various guilds that give you new weapons and new classes that you can level. For example, you can start as a Thaumaturge in Ul'dah (babby Black Mage), but you can also pick up Pugilist (babby Monk) and Gladiator (babby Paladin) in the same city for combat classes, along with a number of non-combat professions - Weaver, Goldsmith, Alchemist, and Miner.
And each citystate has roughly the same number of classes and professions of their own. You usually have to hit level 10ish before you can pick up new professions, though, so you likely just hit the cusp of when you will be able to do that. At around level 15 you'll be able to travel to all three citystates and collect all the base classes and professions on one character if you so desired. Being able to be everything on one character - plus a lot of content being gated behind the Main Story Quest (MSQ) - is why many folks are imply the game isn't very alt-friendly, since you can do everything on one character anyway and you have to do a lot of monotonous retreading if you want to level an alt to a decent degree.
However, there are some reasons to have alts. RP is the most obvious one - having a different character to portray a different, well, character. Some people have alts on different servers to play with different people. And some folks just want to try out being the different races without having to shell out the money for Fantasias (the "redesign your character" item). There might be even more that I'm not even aware of.
My best recommendation is to do basically what you're doing already. Feel out the game in the trial and see if you like the base game itself - since you mentioned you're not certain on whether or not you'll want to RP... it would make sense that you make sure you enjoy the rest of the game at least. Otherwise you're paying money just to sit around town watching people RP at each other. Then, if you decide you like the game and get the full version, then you can see about transferring over.
And if/when you do transfer, I'd at least recommend bringing both Miqo'te and at least one more character (or one of them and two new alts, or even three whole new characters if you decide you want to keep the Seekers on that server) over to Balmung with the transfer. You specified three is you limit, and your uncertainty on whether or not you want to RP. Having the three there "just in case" - you don't even have to play them if you don't want to - will ensure that they're there if you decide you want to take the plunge, and help you avoid having to pay the transfer fee again in the future. Plus, if you get the special edition, you get a free Fantasia or two... so you could even change the characters "waiting in the wings" to whatever else catches your fancy.
... That got a bit rambly, but hopefully it was informative and helpful.
Edit in response to your edit!: Unfortunately, there's not really any marker to imply that you are on trial. However (and I'm not entirely sure you can do this in trial but you might), there is a Character Info block. It's a bit limited in space, but you can use it to identify such things as gear level and RP character summaries. You access it by clicking on the Party icon, right-clicking yourself, and choosing... I think it's "Update Character Info" or something like that. If you examine folks, sometimes their character status window will have a little word bubble icon - hover over that and it'll show you what they put in their info block!
And each citystate has roughly the same number of classes and professions of their own. You usually have to hit level 10ish before you can pick up new professions, though, so you likely just hit the cusp of when you will be able to do that. At around level 15 you'll be able to travel to all three citystates and collect all the base classes and professions on one character if you so desired. Being able to be everything on one character - plus a lot of content being gated behind the Main Story Quest (MSQ) - is why many folks are imply the game isn't very alt-friendly, since you can do everything on one character anyway and you have to do a lot of monotonous retreading if you want to level an alt to a decent degree.
However, there are some reasons to have alts. RP is the most obvious one - having a different character to portray a different, well, character. Some people have alts on different servers to play with different people. And some folks just want to try out being the different races without having to shell out the money for Fantasias (the "redesign your character" item). There might be even more that I'm not even aware of.
My best recommendation is to do basically what you're doing already. Feel out the game in the trial and see if you like the base game itself - since you mentioned you're not certain on whether or not you'll want to RP... it would make sense that you make sure you enjoy the rest of the game at least. Otherwise you're paying money just to sit around town watching people RP at each other. Then, if you decide you like the game and get the full version, then you can see about transferring over.
And if/when you do transfer, I'd at least recommend bringing both Miqo'te and at least one more character (or one of them and two new alts, or even three whole new characters if you decide you want to keep the Seekers on that server) over to Balmung with the transfer. You specified three is you limit, and your uncertainty on whether or not you want to RP. Having the three there "just in case" - you don't even have to play them if you don't want to - will ensure that they're there if you decide you want to take the plunge, and help you avoid having to pay the transfer fee again in the future. Plus, if you get the special edition, you get a free Fantasia or two... so you could even change the characters "waiting in the wings" to whatever else catches your fancy.
... That got a bit rambly, but hopefully it was informative and helpful.
Edit in response to your edit!: Unfortunately, there's not really any marker to imply that you are on trial. However (and I'm not entirely sure you can do this in trial but you might), there is a Character Info block. It's a bit limited in space, but you can use it to identify such things as gear level and RP character summaries. You access it by clicking on the Party icon, right-clicking yourself, and choosing... I think it's "Update Character Info" or something like that. If you examine folks, sometimes their character status window will have a little word bubble icon - hover over that and it'll show you what they put in their info block!
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