Theres a catch to what your looking for. You might stumble into a large trout, 4 or 5 pounds but most will be much smaller. Then I think you mentioned salmon. They come much bigger on the average and you'll probably need a heavier reel, rod and line! Get the rig set up for salmon and you have over kill on trout! Get it set up for trout and it's iffy on salmon! For either fish a 6'6" to 7' rod would work, get a med to medium heavy action rod. Buying a reel, I'm pretty clueless about sizes, especially in spinning reels. Most all my spinning reels are Ultra Light. If I was to go for salmon I'd take one of my catfish rods. The UL rods all have max 4 pound line and are either medium light to UL actions. My cat rods are mostly round casting reel on 7' rods and have 20 pound braid line in them. I did use one in the ocean several years ago using 15 pound mono and got a 24 pound salmon without trouble. I also have two reels that if still made would work pretty well for what you want. Garcia Mitchell 300 spinning reels. They are noticiably larger than any UL reel and really nice thing is when they were new they came with two spools. You could put heavy salmon line in one and light trout line on the other. As for the rod, a medium might be the best compromise for both spices of fish and about 7' should werk well. Then switching from one fish to another, simply change spools. I had a small Pflueger spinning reel with an extra spool but don't remember where I got the extra spool from, probably Pflueger! I have one more spinning reel that might work for you. It's a Daiwa J-25. Pretty big for a trout reel but I'd take on a salmon with it on say a 7' mediun heavy rod of some kind. Over kill for trout in my book but you could catch them with it! Might even get a second spool for this size reel from the manufacturer.
Lot of guy asking about rods for catfish don't ever seem to get getting a set up for the size fish you are targeting. Bullhead is a cat and I've never seen or heard of one over 3 or 4 pounds. Then a Blue is also a catfish and the record blue is over 100 pounds! One size does not fit all. I have recently set up a couple low profile casting reels mainly for bullheads and small mouth bass. Size of the fish range from maybe 8" to several pounds. I could do either with one of my UL spinning rod/reels and 4 pound line! Best to set the rod and reel up for what you think your average size might be. My advice to you is get an UL spinning rig, come a set in most places, for trout and maybe panfish and for salmon get a larger rod and reel for the salmon. Light line 4-6 pound for the UL and maybe 15-20 pound for salmon. Don't be overcome with the you get what you pay for croud. That 24 pound salmon was caught with an ABU 6500 reel and a $25 rod! I also have a very inexpensive round reel by Shakespere that has plastic gears and wouldn't land as many 24 pound fish as the ABU but would do several on that same $25 rod for maybe a quarter of the price or less of the ABU!