Your budget may not be able to afford it at this time, but it sounds to me as though you may need two rods. The 4 or 5 weight would be good for panfish and trout and the 7 or 8 weight for steelhead and smallmouths.
If one rod is all you can swing at this point, you may want to consider something between the two, like a 6 weight. A compromise, yes, but it could get you started quite nicely. And, it would be great to learn to cast with.
When you are ready to add another rod to your arsenal, you can then move to either the 4 or 8 weight, depending on what you tend to be fishing for the most.
By the way. I wouldn't bother to learn to cast at this time of year. What I would recommend is continue to study and read a lot. Research all the various equipment out there, go to some fly shops and ask tons of questions (even if you have to travel an hour or two to get to them), and get as many of your questions answered as you can. Hit all the fly fishing forums on-line as well and ask questions there. Then, in early spring you can take a few casting lessons and make a more informed decision as to what type equipment you really want.
Hope this helps.