Food, Challenge Log, Squadron Buff, Roulettes, Heaven on High, and doing your job quests should be the main ways of getting xp. By when you reach 70 progressing through MSQ should be a breeze.

Remember that while a high majority of people are going to playing in Shadowbringers content the game is open to everyone, those going through HW and SB still. So queues will still be active for dungeons and hitting those MSQ dungeons will be worthwhile.