re: About to take on more responsibility at work, best ways to approach a raise...

Document what the increase in responsibilities and then go out and find the pay ranges for that position, and your current position. Numbers are a great influencers.

I hope the best for you but I am guessing you are going to get screwed on this, since you were likely underpaid already. Why would they give you much of a raise.

if the numbers don't work, ask him what you need to do to prove your worth. Document that and revisit in 6 months.