Well firstly no need to buy gear, so long as you have got some tome gear to meet the min lvl req of the first dungeon you can get more gear from there in EW. Save your money. Trials etc are not going anywhere, but the writer suggested we do the Omega raids for the story as well as somethiinggg else.. I forget which :x
I would focus on doing the story related suggestions so that the endwalker story hits home as hard as it can! The other stuff is all optional and can wait. If you do want a shadowbringer relic that would be the only one to try and get done sooner than later as I expect that content will die for a bit when endwalker first hits since ykno, everyone will be busy with msq for a while!