I saw the previous I1a thread here but the latest posts to it are several years old, so I will begin a new thread.

I just received my test results from Nat'l Geographic, transferred them to Family Tree. Nat Geo said my y lineage is I-Z74, F.T. says it is I-CTS1321.

Grandfather was Karelian Finn. I'd like to get some further tests to try to refine this heritage, for example, most Finns are the (old) N3 haplogroup so how might I interpret an I1a result for a Karelian? My test results seem to be a LOT (like, 12,000) of SNP's, should I try for some STR's and if so, which ones?