You should start on your relic quest (talk to an NPC in Vesper Bay to begin). That will lead you through basically all the endgame that existed prior to 2.1. The quest in particular has you doing Amdapor Keep (A dungeon people farm for myth tomes. Hit 450 each week!), and the hardmode primals. As you work on the relic weapon quest you should get a primal weapon (Preferably Garuda, but Ifrit can work too), and have most of your gear upgraded to ilvl 70 Darklight by the time you beat Titan hardmode and unlock your relic weapon.

After that, you can work in Binding Coil of Bahamut. The aforementioned gear to beat Titan (Plus relic) should be decent enough to start on the first couple turns, but you WILL need most of your gear at 90 to finish it.

As far as mythology tokens, upgrading your weapon and shield to the 90 versions takes top priority. After that, either buy accessories if you have multiple 50s that can use it (I did, as I had both WHM and SCH 50), otherwise pick up the main armor pieces.

Now, patch 2.1 added a lot of new content. Crystal Tower sits at about Garuda level IMO, so you can tackle it with a 55 or 60 weapon and some darklight here and there. You can get level 80 armor here. Good King Moogle Mog is about on par with Titan hard, both drop level 75 weapons. Ultima hard mode is a little above Titan hard mode, drops level 80 accessories. Extreme mode primals require that you beat all the hardmode ones first (same requirement as binding coil), so take a wild guess where they sit. They drop level 90 accessories and beating them all can get you a level 90 weapon.