Realistically how many jobs can I level at once with the XP boost

[Archon]

Luckily I made my char on a preferred server before they did away with all preferred. I'm now hitting a wall doing Arcanist AND Pugilist where I switch in between main quests but I'm still outleveling the quests by quite a bit. Should I pick up a THIRD job?

[TheSuit]

Pretty much all of them, except craftng \ gathering. Since both of those are heavily time dependent.

[Sevrojin]

once a class hits level 50 all other classes below level 50 gain +100% exp
get a class to max level 80 all other classes 50+ gain +50% exp
rested gives +50% exp
pre order earring gives +30% exp
free company bonus can give +15 % exp
food gives + 3% exp
not sure about prefered exp or the new player bonus thing

all of these add together for some pretty serious exp gains

[Kitsune]

Depending entirely how much you're willing to play, you can do every class to 70 and every crafter to 80 if you want within 30 days.

I can't find the screenshot of my having all crafters 80 on this character that I took on the 31st day playing on this alt. The goal was to become a mentor while being a sprout, lol.

https://imgur.com/a/MW48N9P