Interesting fly, this beadhead adams nymph. I fish dry adams quite a bit, but I've never used it as a caddis imitation. In my mind, an adams is a generic mayfly imitation. I tie mine exactly the same way I'd tie a BWO or PMD or Hendrickson, just with different colors. Floats as well as any of those.

That being said, that beadhead version looks like a fishy nymph.

I own a couple of 3wt rods I use for trout in small streams. Casts medium to small dries and nymphs just fine. Even small streamers work OK.

If you're gonna use it where there's a possibility of catching larger fish, keep a couple of things in mind. 1. There's a chance you might break your rod. 2. There's a chance you'll kill the fish since you'll have to play it longer than you would on an appropriately-sized rod.

If you can live with these risks, go nuts.