Look for the same qualities in a modern salmon reel. Rules for loading a salmon reel are the same as for trout - fill it to the brim, but not so much that it jams. You can get lot of flexibility from a single trout rod reel. Chose your rod and then your reel then buy at least 3 spare spools and lines to fit that reel before you buy another reel. When you get you next reel, buy the same one, that way its all interchangeable.
Reels tend to be forgotten in the bottom of a tackle bag and can take a bashing.
It's worth investing in a proper case. Spare spools are useful, but you are much more likely to have 2 set ups for salmon fishing. A sunk line rod and reel and a floating line rod reel. One solution I like for the less affluent among us is the loop to loop. At the business end whip in a large loop.