Hello Tim,
That’s a tall order for one fly rod!
When it comes to fly rod weights, there are three things to consider. One is your ability to fight the fish. Second is being able to comfortably cast the size fly you need. And finally how big are the waters you’re fishing. A typical Brown Trout might be 12 inches long and looking for a #14 fly. A smallie might be 16 to 18 inches and wants to eat something a lot bigger, like a popper tied n a 1/0 hook. And Steelhead while might prefer a small fly at times, but you will have your hands full when you hook one as they are large. Are you fishing small streams, bigger rivers, or lakes? Lighter weight fly rods work well on small creeks and streams where you need to be stealthy. Out on a big river or a lake, a heavier weight rod will let you throw a big fly into the wind without tiring yourself out.
Right now, the majority of fly rods meant for Trout fishing are 9 foot 5 weights. That seems to be very popular size. Smallies could be covered by anything from that same 5 weight up to an 8 weight. I fish the upper Mississippi and the St. Croix, big water ands big fish, and an 8 weight is a lot easier to use over the course of the day. A lot of guys fishing Steelhead are using 7 or 8 weights, and a reel with a good drag. So as you can see, one size doesn’t fit all.
If you’re just starting out, a 6 or 7 weight might be a good compromise. It’s a little heavy for Trout but it would work. And it would allow you to throw bigger streamers or top waters for Bass. Steelhead are a species I don’t have a lot of experience with (in spite of considerable effort on my part) but a 7 weight would work. A 6 weight might be a little light.
A 7 weight fly rod is a lot like a 6 foot, medium weight spinning rod. It’s an all purpose tool that convers lot of situations, while not being optimum for any of them. I still have the first 7 weight rod I ever bought.
Have fun and good luck with those Steelhead!
SR