Level 675 gear upgrade

I have a level 100 character, but have not yet finished the MSQ, currently on l98 quests of that.

I can run the daily l100 dungeon through duty finder to get the tomestones of Heliometry, but am I right in thinking I can't spend them until I finish the Dawntrail MSQ line?

If this is right, is l675 the current max for me?

Sorry for the stupid Q, returning player here and all of the tomestones etc have changed since I last played properly/last needed them.

TIA