Flying FI KEF-SEA transferring (same ticket) to AS SEA-SFO:
1. Is 1h25m international to domestic transfer at SEA normally doable? (I have Global Entry.)
The timing seems good to me, but those who have done this transfer recently can say more. You will get your bags, do the GE thing, check your bags onward, and then exit to the A concourse for your connection.
2. Do FI & AS operate in same terminal? Or will there be a long walk between terminals?
SEA thinks of itself as one terminal (all gates available inside TSA), but there are several concourses (one of which is S, where you will probably arrive). Once you are in the A concourse, given that an Alaska flight will (almost without exception) leave from C, D, or N - go to the "train" station near gate A3. Go down to the train platform and take the "yellow" train on the right to the D concourse. If your connection leaves from D, go upstairs and to your gate. If it leaves from a gate at N or C, cross the train lobby and take the "green" train to the relevant concourse. Go up to the gates and you'll be set.
3. After baggage retrieval and customs, is there a transfer desk to drop off my bag quickly? (A couple of years ago at PDX, there was no transfer desk, and so I had to take my bag upstairs and recheck it at the AS check-in counter, plus obtain new boarding pass.)
Check this out:
International Connections | Port of Seattle (portseattle.org)