From: https://www.wowhead.com/news=316229/...in-shadowlands
In Shadowlands, new players will need to go through Battle for Azeroth as their first leveling experience. For veteran players (or new players that leveled a character through BFA at least once), you are able to select what expansion you want to level on! Chromie can be found near the embassies in both Stormwind and Orgrimmar, sitting on top of her big hourglass.
Short answer: Yes

Heirlooms still have upgrade levels. The bonuses are good, particularly because out of combat regen has been drastically reduced from where it is today. Also makes it so you don't have to worry about finding quest upgrades. The levels will come much quicker than the upgrades for 10-50.