I'd suggest that you get a new chain to go with your new cassette. A chain with significant mileage is likely to not play well with a new cassette. I prefer a chain with a quick joining link to the Shimano "special joining pin" concept.
A fork mounted cable hanger will help you to avoid brake shudder with your new cantilever brakes. Problem Solvers Wide Cable Carriers http://problemsolversbike.com/produc..._cable_carrier will ease adjustment and centering.