Stuff which still is useful till today:
OOW MPG Trials: Trials which will give resi stats otherwhise not available. there are 6 trials which in total will add 50 to all resis. Look for Proving Grounds: The Mastery of Efficiency and similar on alla. there are 2 sets of trials one set of 6 is grouplevel but there is another set of trials for raids. Don't pick the raid ones
DON: gives stats and a buffslot. You can't do all without a raid, but nowadays most of it should be doable with a group.
Gear: nothing better than global dropping Defiant gear til level 80. Next droppable than would be "Archaic xxx" which is already SOD Entrylevel gear with foci to lvl 85.
Once lvl 80 and some new gear, if you have a group, you will be able to start SOD-Progression.
Progression:
For SOD than you need to take your time. I would suggest to do all the progression to get the best of this expansion. You will also try to get most of the gear of SOD befor you will be able to handle the Underfoot-stuff. A possible shortcut for the gear would be the new tradeskilled gear from Underfoot: "Stalwart xxxx". Requires lvl 81 and its level of gear is slightly better then best SOD-gear you can get.
For the non-visible slots, if you can stand it, there is a Boomerang mission in Brells rest. This covers most inivisble slot. levelrequirement of that gear is lvl 80. But you can get in the "mission" earlier.
Setting foot into Underfoot content requires a solid base in AAs and gear. Unterfoot starts where SOD ends, there is no overlap as there has been in the past, allowing to skip some of the previous expansion.
AA vs. lvl:
If you can mangage to gather a group together I would not rush to lvl 85. Take your time and adventure a little along the expansions. A shaman can get away with not so much AAs, but your tank will need a lot of them nevertheless. At level 70 with some defiant gear and buffed in GL with lvl 85 buffs gives the possibillity to do AAs faster than lateron.