Right, after Praetoria Proper you take the Imperial Underground to First Ward and on into Night Ward. There's access to the AE via Studio 55 (and now a new access point in Nova Praetoria). Once in Pocket D the SBB can be done, a handy boost. Provided they start from within Praetoria or Pocket D the Cathedral of Pain and all the Incarnate Trials are possible. Belladonna Vetrano's arc is doable provided it is taken from ouro and you physically go to Night Ward to enter the mission. And speaking of ouro, if you have a crystal in your base all the arcs you missed along the way are open to you.
(And as per my sig I've written a trilogy of Loyalist AE arca and a trilogy of Resistance AE arcs, level 19-25, designed to be playable just at the end of Neutropolis but before going to First Ward or taking the Rift. Also designed to slot into canon.)
Then holiday events, and all of that. Apart from the Valentine missions, which are just not doable.