Well I don't add additional weight when casting spinners as it may affect the action of the spinner, it also can make casting more of a pain.
If you want to cast farther use a kastmaster lure or increase the weight/size of the spinner. That said there is a lot of fish that can be in close and don't require a long cast.
I don't recommend tying the line right to your lure, I use a small swivel as it makes changing lures much faster and more importantly it helps with keeping your line from becoming a slinky from all the twisting
As for your rod being big enough to fish rivers, just be aware that you may hook into a BIG fish and loose your lure and some line...... or have a long fight
I routinely fish rivers with my 8' 6" spin/fly combo rod and 6 lb line. I also use a ultra light rod to fish smaller rivers and streams, if I remember right it's closer to the 5'6" of yours. it makes it a lot more fun to fish for panfish and smaller trout.
Hope that helps! Bob