If you were buying completely piecemeal for 1K, what would your list look like?
Hmm... that's a good question.
Honestly, I think the "rule of cool" always applies for anything you buy. If you like a mini, then buy it and try it. If I were starting over, I'd seriously consider 3D printed lizards from other companies. One Page Rules, Raven Twin Miniatures, Lost Kingdom and Last Sword Miniatures each make a whole range of cool looking Seraphon alternatives. I'm also fond of the space lizards from Clay Beast Creations. However this would possibly rule out playing at your local game store and definitely rule out GW tournaments.
I think it might be more helpful to suggest versatile and commonly fielded models as opposed to a shopping list for a 1K army.
-A Slann is a good purchase. It's effective in both Starborne or Coalesced armies and will likely see plenty of play on the table.
-Stegadons are effective monsters, and the kit is very versatile. You can build it as a Stegadon, or a Skink Chief on Steg hero, or an Engine or the Gods hero. Honestly, the model is fairly easy to build so that you can swap out to any of those options. You see Stegs more in Coalesced-Thunder Lizard, but the EotG can easily work in Starborne lists. You could only fit 1 into a 1K list, but more are good additions down the road.
-If you buy a Slann, then Saurus Guard are the next purchase. The box gives you 15, and you can use them all, but you technically only need 5 to help protect your Slann.
-An Astrolith Bearer helps a Slann (or any Seraphon wizard) and is useful for either army, but probably more for Starborne. If you buy the Guard, then I'd consider using one of them to build an Astrolith Bearer proxy. I think someone from the forums even created a free Astrolith 3D file that fits the Guard's standard icon. If not, then buy the actual AB model.
-Skink heroes are all useful, but I'll mention 3 of them in my order of importance. The Starpriest has a great ability that can help any unit generate mortal wounds and has a good spell. The Priest has access to a prayer and very useful abilities to help any Skink units. The Starseer again has a handy ability to boost charges for any unit and also has a good spell (you often see this model in Coalesced armies to speed up Knights). *Honorable mention* Since you used the Oracle in your list, I'll say that I love the model, but it's a bit of an odd duck. It has the same spell as a Slann and is a decent wizard on a monster. But it really seems like more of a casting platform for Slann, and is arguably most useful when fielding Lord Kroak.*
-Skinks are probably the next best purchase. You'll need 2 boxes at least. People generally build them with boltspitters/blowpipes and shields.
-Salamanders are a powerful unit, in Starborne especially. I'm not a big fan of the model, so I don't have any. But there are some cool 3rd party versions as I mentioned earlier. For 1K, you likely only need 2-3 Salamanders.
-Bastiladons are another good Coalesced-Thunder Lizard monster for Seraphon. Again, people generally build it with the Solar Engine, but the Ark of Sotek is cheaper.
-Saurus Knights are the best Saurus troop unit, and they are good in Coalesced lists. If you go that route, then you'll need 2 boxes.
I still think the Start Collecting boxes are good values, and one added here or there is a decent way to get a mix of units. In the Start Collecting Skinks you get our most flexible battleline (Skinks), a good hero (Starpriest), some flyers to try out and a good Thunder Lizard monster (Bastiladon). In the Start Collecting Seraphon box you get a good Saurus battleline (Knights), a cool looking and decent monster hero (Carnosaur) and an adequate battleline (Saurus). You can actually build more from that box. Check out this thread to get the most from your
Start Collecting Seraphon.
I hope this is helpful.