Guns would completely ruin the feel, I'd agree with crossbows, all with their own unique designs.. They would start off with Iron & end up with Daedric - But! I personally think they should be on a leveled list only AFTER you've found the design handbook for them, attach a script that would add the recipes to your list once you've found the designs, could be like the Spell Tomes DLC from Oblivion, you can only unlock certain bows after finding the designs.. you get the idea :) But, yeah.. Crossbows all the way.