Leader to braid questions

I haven't been fishing long, late last summer to now, and I just got my first baitcaster for my birthday (Shimano SLX XT and SLX rod). I plan to rig it up with 30lb braid since I don't fish very thick cover, just ponds and some lakes. I am a broke college student so I can't really buy good fluorocarbon so I want to use a mono leader instead so I'm not cutting my braid for both cost purposes and keeping a full spool for casting. I've heard to use upwards of 40lb, a lb lower than your mainline so it snaps first, and I've heard match diameters of the line (8-10lb mono to match 30lb braid). So my question is, what pound mono would you guys recommend?