Returning to Eos after Aya is a fine move, as the radiation on the planet will have died down considerably, allowing you to complete just about every quest on the planet and explore it thoroughly. It may not be as sexy as setting up new outposts on Voeld or Havarl, at least you don’t have to share the place with the Angara. It’s a good place to start really taking out sidequests, although it’s worth going over Eos in general, first.
After completing “A Better Beginning” and getting the vault on Eos up and running you should have explored a bit - namely Site 1, the three Remnant monoliths, the vault itself, and perhaps you bothered to deplete two Mining Zones, as well. That being the case, the center-east section of the map should be fairly revealed and familiar, and it makes sense that you’ll start with quests in that area. Not coincidentally, this is also where the lighter radiation was pre-Aya. Yep, radiation was merely a plot device used to keep you temporarily constrained, and to give you good incentive to hit that vault.
The radiation isn’t the only thing that’s changed on Eos however - as much as the radiation has decreased, Kett activity has increased in response to the more favorable conditions. Expect to find new Kett camps set up in areas that were previously clear, and basically everything west and north of Prodromos is Kett territory - clearing out the more substantial of these Kett strongpoints will make significant progress towards Eos’s long-term viability. Aside from Kett and Remnant, on Eos you can expect to face various insectoid wildlife, like Spitbugs, Shemrys and Kaerkyns, as well as the “mammalian” Challyrions and Taurg. Near Kett installations in the Presson Dunes you may also have the misfortune of finding Fiends, to which you’ll be properly introduced during the quest “The Secret Project”.
You will, of course, also find plenty new Mining Zones on Eos, which can now be easily mined as you find them. Unfortunately for Eos, its mineral wealth isn’t great - you’ll only find Aluminum, Graphite, Iron and Vanadium on this planet. The latter should easily be your primary target, the rest are easy enough to accumulate over time via the Mining Operations perk. To scour Eos properly for Mining Zones, just hunt down Forward Stations (which should come marked on your map), as deploying them will reveal nearby map markers, including Mining Zones.