#1, if I were to put a new speaker in it, which I am, would I be bale to put one that is more than 50 watts in it and #2, what speaker would be good for shred and metal?
yes and yes

Speaker upgrade is a nice big jump. Vintage 30 is nice but there are some other speakers out there that will work better at a lower cost. From what I've seen, a warehouseguitarspeaker.com Veteran 30 or something like a Eminance Swamp Thing or Man o War would work well in this amp. Range: $65-95.

Overdrive pedal is a must. EQ pedal is nice to have too. Visit the VK thread if you like. First couple of pages and then last several pages then post.