Is it silly to level an Alt?

[Memoe]

Lol you should see my face. After lvl 15 there's only one questline?

And the thing about levelling different classes on the same character. Does thst mean I can have a lvl 50 Gladiator, but if I give him a bow he turns into a lvl 1 archer?

How are we supposed to do it? Do a bot of conjuring, then switch to pugilist for a level or two, then switch to the pet class, etc?

The main questline will be a long, but there are a lot of side quests and ultimately class and job quests tied to all disciples respectively.
Yes, you can have a lvl 50 Gladiator, and when you equip a bow, he will turn into a level 1 archer if you haven't leveled archer before. You can have all the classes to 50 if you level them. You can change class by simply changing main hand equip.

At later time (around level 30) you'll get Jobs that those classes evolve into, but they will be explained later. For a Job you need to have the main class (say gladiator) to 30 and a sub class to 15 (for gladiator that would be conjurer). That would make you into a Paladin, which is Gladiator's Job. After getting the Job, you will most likely only use that.

Is there enough content to level all classes on the same character? Can we 'outlevel' content?

Eco

There are many ways to level. There are many, many quests, but ultimately the easiest ways to level are doing FATEs (the blue circles around the map) that match your level and dungeons (in which you also get loot). You can't outlevel content by much, as your level will be lowered during FATEs or dungeons that are way under your current level.