First, welcome to the game.

Just so you're aware, you do need to reach level 50 and complete all the base game's main story quests before unlocking the 3 new jobs (they require you to be able to access Ishgard, which is some 100 quests from the start of the game).

You do have an option to change your race using fantasia bottles. You get one free bottle when you first pay your subscription (usually 1 month unless you buy a time card), so you can play around with your lalafell and then change to Au'ra later. It will retroactively change all the cinematic scenes so you can watch it again later. It's not quite the same I know, but it's an option if you're unsure.

Otherwise, you can make both characters. You do have to pay a slightly extra fee or subscribe for 6 months at a time, but it is an option.

Race choices are almost all about aesthetics only. Endgame stats don't matter at all. Also, which classes did you play back in WoW? Is there any particular class or playstyle you like from that game? For example, the Summoner is similar to the WoW Warlock in FFXIV, and Bard ends up becoming much more caster-like after level 50 because of charge times (which some players find disagreeable).