There’s a lot of ways to stain, but if you can start finishing with a plan thats easiest. Once you are sanded, wet it down with water to saise the grain and sand again, but while wet you should get a sense of the color—it’ll be a little darker when freshly wet with water on it than it will be when finished. If it looks good and evenly colored, probably no need.
Refinishing stocks that had a different stain on them previously, what I found works best is actually to put several coats of plain finish on the stock and let it fully cure. At that point you’ll be able to see if there are weird color splotches or patches left over from the previous stain, or from some of the previous finish left in the surface of the wood, or if there is sap-wood in the stock that needs colored to match. If it looks great, just finish with your topcoats and you’re done. But if you decide to stain, then you can cut it back to wood using water as a sanding lubricant, apply the stain or dye on the bare but filled wood, and then topcoat over that. It’s a bit more work to apply a stain this way, but on fairly open pored wood like you typically find on factory stocks, I think you wind up with a better color than if you used a stain right on the un-sealed wood.