Forging weapons in Three Houses

I've been playing Fire Emblem Three Houses for a while now and I just realized you can forge weapons into new and better weapons. What would you guys say are the best weapons to forge? Is there some kind of guide that shows you what weapons you forge? Also I seem to be lacking a lot of resources or materials for forging and repairing weapons like Wootz Steel and others. Where or how can I acquire those resources?