Re: how to tell rod weight?
If you have some different weight lines, just try them out on the rods.
If the line is too light, the rod will feel like a broomstick, i.e. it won't bend much, even with quite a bit of line out.
If the line is too heavy for the rod, the rod will bend too much. On the backcast, when you start to make the power stroke forward, you will feel the rod "bog down", i.e. lag, feel slow, unresponsive, rather than snapping forward.
"Just right" is in between. The rod should bend some on the backcast, but then snap forward when you make the forward cast.
There is some personal preference involved. On a particular rod, some may like how it casts with a 4 wt line, and some may prefer a 5 wt line.