PvE gear question

I've recently hit lvl 80 and have been doing RDF for emblems of triumph and grinding Northrend reps. My question is should I buy gear in Dalaran for emblems of triumph (in my case Koltira's set) or can I skip triumph gear and start earning emblems of frost for BiS gear?

You must get tier 9. You can not skip it. How else would you be able to raid and get t10? T10 takes a long time.
As a fresh 80 do fos/pos, get rdf hc on farm and get your t9 set and when you have eofs you upgrade.
EOF comes from first daily RDF HC of the day, from voa 10/25- which needs you to be 5k-5.2k gs-, Icecrown Citadel Bosses-which again, you need items to get into- and weekly quest :). So it takes some time to gather EOFs.
If you have gold and want to speed things up buy BOEs, watch out though, they are expensive.

Thanks for your answer!