Sign Language for Toddler

My son was diagnosed with expressive speech delay several months ago. He's now 2 and the early intervention teacher wanted to teach him PECS. After beginning to use it, I noticed he picked it up so dang quick and I began feeling like it was not the best tool for him. I asked to put that off for now and focus on teaching him sign language since I think a) it's more convenient, b) he would learn it just as quickly, c) it will help him with the frustration he's showing when he's unable to talk.

So, we've been doing it for about 1 week now and my question is how quickly should he be picking up signs? While he isn't consistently using them yet, he has shown the signs for more, all done, milk, and banana. Is this a good pace?