I'm not exactly sure how old Liam Edwards is; he could potentially be available for the under 20's next year...  As you say missing out on the Under 20's isn't really that bad in any case, many quality players didn't even make the under 20 team (Tim Nanai-Williams immediately comes to mind).  Indeed there are two players in the current Otago squad that missed out on the under 20's this year (Gareth Evans, Hanipale Galo).  I'd expect Galo may make a big impact in the ITM Cup this year too - he's a 1.91m, 106kg centre with plenty of speed...

Buxtons best position is fullback, but I suspect we will see him playing mainly on the wing (along with Joe Hill) as Otago doesn't have a huge number of options on the wing, but plenty of options at fullback (we may see Galo play a bit on the wing too).