What profession for mesmer
1) Tailor for armour and artificer/weaponsmith for weapons would cover you pretty well though really the only ones to avoid would be leather worker, armoursmith and huntsman.
2) Artificer and Cook are the only ones likely to make much money long term since they produce consumables but really, no crafting makes any money to speak of.
3) Start whenever you want, leveling crafting to 400 is a good source of xp, the first guy to legitimately get to 80 in this game went from lvl 60 to 80 by crafting.
I went tailor/jeweler while leveling.
The main goal was to find two trades with minimally overlapping item requirements. Most weapon skills and armor skills seemed to need plenty of the same ‘rare’ ingredients; trophies, blood, bones,venom sacks,etc.
Tailoring and Jewelcrafting had minimal overlap while both being useful. cooking fits this niche as well.
I would 100% recommend Tailoring and Jewelcrafting for any new players. Keeps a huge bulk of your gear up to date, easy to level, and doesn’t require too much back-tracking to double up on materials.