Congratulations on picking up an extremely frustrating, expensive, and eventually rewarding habit.
There is no one rod that works in all situations, but a 5/6 is very versatile. What weight rod you need depends on several factors, most notably size of fish, volume of streamflow, and size (weight?) of flies being used . I have found that, to fully cover your bases in this area, you probably want a 4-wt. for most of your trout fishing and an 8-wt. for salmon and steelhead. A 5/6 is ideal for larger trout and small salmon (pinks, for example), and it is also good for trout on larger streams. I fished with only a 6-wt. for years, and I usually found it to be too heavy for trout and too light for the big fish. That said, I caught a lot of fish on that rod, and it served me very well.
Eventually, if you decide to stick with it, you will want to buy a couple more rods. Whatever you buy, make sure you cast it first. You will generally (but not always) find that the high end rods are clearly superior tools, but there are several solid rods available today in the $200-$300 range. Redington, for example, makes some great rods, and their high performance models offer lifetime warranties (another essential thing to look for, as you WILL break rods over time). Reels are another subject altogether, but since you don't have to worry about how they cast, you can find one you like at a local retailer and then hunt for deals on eBay, Craigslist, etc. When it comes time to buy lines, go to your local fly shop. They will set you up with the right looping systems, etc. For that matter, buy at your local fly shop whenever possible. They need your business, and they will always take good care of you.