A couple things to add, like an above poster stated, low level roulette is still a great option for leveling, because of the XP bonus for completing it, not only just for post 50s.

Yes I would recommend to level your gathering and crafting classes together. Botanist goes well with Culinary/Weaver/Alchemist/Carpentry. Miner with Blacksmith/Armorer/Goldsmith. Leatherworking can be leveled with any DoW/DoM.