In terms of a hook line, for me that came around level 15ish during the main questline in the story. I am not sure if story is important to you, but if it is, I would wait for that part and maybe run a dungeon or two to get a better feel. This game is also better IMO (as many others are) if you play with others.
I'm pretty sure you get 30 days free with the initial purchase and there are no subscription 'tiers' except for some pricier ones allowing you to create more characters per server.
Starter armor is all race based, most of it is pretty good looking imo though can't be dyed and won't necessarily match your class. I see pieces of it used as glamour at 50 quite regularly though.
The options for the game are very extensive. You can change it so that equipment rewards from quests or obtained from dungeons/etc are deposited directly into your inventory if you so choose, don't recall where offhand but there's a ton of settings that can adjust all sorts of nifty things. Worth poking around in there.
The 'public event' is a FATE, "full active time event". They spawn all over every map in the game pretty much - mouse over them for progress completion and estimated level. Participating in them rewards XP based on how much you contributed, they're worth hitting up when convenient but you will have enough quests and XP bonuses to not need to grind them really. I'd highly recommend following the story quest and your class quests (from your class guild) and reading the tutorials they pop-up for you, it will introduce almost all of the basics as you go.
Hook for me was crafting. Additionally all the combat classes tend to become more interesting to play around mid 20s imo when some more useful/fun buttons unlock. Then at 30 you get your 'advanced job' which helps a lot as well. Further levelling multiple classes has the benefit of certain abilities being able to be 'equipped' to other classes - for example the marauder ability 'mercy stroke' is a useful ability for other damage dealers as it costs no TP and doesn't trigger the GCD, free damage basically.
There's constantly FCs (aka: guilds) and LSes (aka: custom shared 'chat channels', kind of like a 'community') recruiting in most of the major cities (Gridania, Limsa Lominsa, Uldah). There's no penalty for joining/leaving - no harm in messaging one of them. Lots of folks are still out there levelling ninja/alt jobs.
I'm gonna start a new toon
You know you don't need to do that right. You can change your class just by equipping a different weapon, modify your appearance in game with aestheticians, or completely rebuild your character (race, gender, etc.) with a Fantasia (I got 2 for free, but I think they cost real money beyond that).
And someone asked above, you can pay for server transfers as well.
So i'm pretty sure I just finished the main scenario, but patch 2.51 was supposed to have the second half, wasn't it?