if I remove the drum brakes on my trailer and replace them with disc do I have to remove the residual valve ? if so how do I remove the master cylinder ?

On my trailer I was able to order and replace the whole tounge assembly with the correct master cylinder already in place. All I had to do was remove three bolts and the brake hose. Reassemble and bleed.

Depends on your coupler, but probably, here is a link that has alot of tech help. should answer alot of questions. http://www.championtrailers.com/techsup.html