It is really whatever you want. Crafting generally won't have a meaningful impact on a character in SL and the crafting economy is pretty saturated at this point in the expansion so things are cheap and gold making opportunities are limited. Alchemy and engineering can be useful for keys and raid but aren't required.

If you want old transmogs then blacksmithing will let you craft the plate you want. Keep in mind crafting is broken up by expansion so you would need to acquire recipes and level each version of the skill.

Otherwise, wait and see how the Dragonflight crafting system adjustment/rework/expansion develops over the beta and pick what you like.