What size hose do I need for a vacuum hose my line broke running from pump to firewall 

I think its 1/4" nipple size for that main vacuum line. 

Ok could a vacuum leak cause my truck to leak oil

It could add to your current leak. When your vacuum pump turns it sucks air in so if there is no line attached to it it will pump air in crankcase creating more blowby. 

Alright will rubber hose work

Most parts houses have the plastic line. Take your old piece to one, they might have what you need.