I'm not forcing OP in any way to use one method or another, merely pointing out the pros and cons. If you want to take your time and play the game, go ahead and do so. Players who ask for advice do not need to be told to take it slow; thats what they're already doing. Players, especially new ones, should know just exactly what that means, and a person new to MMOs should definitely learn just how MMOs work. Maybe you are okay with mediocrity and never improving or changing, but I for one want everyone to be their best, play their best, and know what they're getting into. OP asked for advice, so I assumed that they're somewhat interested in self-improvement. If you read my posts you can see that I don't care what playstyle you choose, I only care that you're educated about the nature of the situation and not simply wasting your time and money.
You two seem to feel fine oppressing new players and keeping them unaware about the bigger picture.
Peptaru not sure why you suggest its favorable to wait for content to be outdated before you experience it. That is awful advice and that is essentially robbing the OP of very valuable and fun experiences. Why play the game now at all? Just wait a few more years for expansions to come out lolololol
In any case, I still highly suggest getting one character to level 50 reasonably quickly, and then play however as you want with future characters/classes. Once you have a Lv50 you can go back and play slow-mo on another class or character if you want, and still have the option to make gil quickly at anytime, and still have the benefit of experiencing the game with the vast majority of its players.
What you are suggesting is for them to waste another month or two's worth of time and money doing something that can be done within a week, without all the options and bonuses above.
Go fast, go slow, doesn't matter, just know that if you go slow you put yourself at a severe disadvantage for every single bit of content in the game. Less players queueing up for those dungeons/raids, less people doing FATEs, less gil to earn, etc. Eventually if you're too slow then content becomes outdated as people outgear/outlevel it and then by the time you get there, you're not even experiencing the content the way it was meant to. Sure this might not matter to you, but new players should still at least be aware that consequences like this exist.