Races have different starting stats, but equipment more or less erases those and they are extremely negligible. Play what you like race wise (90% of the servers are female Miqote and Au Ra lol). Your class determines your starting city.
Classes you start with a base class. Around 25-30, they evolve into a new class. For instance, rogue -> Ninja, Pugilist->monk, gladiator->paladin. For Heaven's Ward, you can pick some new classes like Dark Knight, Machinist, etc around level 30 (which is odd, because you cannot unlock HW until you beat the regular main story quest which goes to level 50). At level 50, you can pick Samurai or Red Mage if you have Stormblood. The HW and SB classes start at 30 and 50 respectively in terms of what level the job/class is.
Link to page with info
Class - Final Fantasy XIV A Realm Reborn Wiki - FFXIV / FF14 ARR Community Wiki and Guide
All the classes play fairly differently. Bard is a ranged DPS class and they have buff songs. They are currently a really strong pick. I main samurai and monk currently (both melee DPS). All the healing classes can also DPS (especially summoner...summon bahamut = GG DPS meters). You can switch jobs once you hit a certain level...I think 10 or 15? You literally can pick every class in the game and level them if you want. You don't really need alts in this game, one character can level every class/job and swap between them at will. Inventory management becomes the rough part with lots of dif roles lol.
Crafting is also like any regular class...you basically turn into a crafting/gathering class and have to level it. Some people don't like it, but it is somewhat interesting and you'll make a fuckton of money if you put effort into it.
I don't think there is a forum guild. I'm on Marlboro myself. If you notice, the game has a list of preferred servers. If you create a character on a preferred server and end up subscribing, I think you get some really nice XP boost bonuses and some starting stuff. Join a guild (called Free Company). Active ones have guild buffs which give you XP bonuses for leveling. I got invited to a random one on my server when I was new and they are really active, be it casual stuff and they have some raiding groups for those who want to do that.