It's good to have the buck smaller than the doe, as brood does tend to have less trouble in labor. First time litters, especially with Holland Lops, tend to not go as planned for various reasons. Between 6-9 months is a good time to breed does for the first time. They can be bred until they make it obvious that you're done, normally around the age of 3 - 4. Bucks can breed effectively as early as 4 months of age. I have heard of bucks that are still breeding at the age of 6 - 7!
I could go on and on, but that is really up to you how much you want to research and learn. Please do not breed without a purpose, there are plenty of rabbits in shelters if you are breeding strictly for pets. People may find it kind of ironic I'm saying that, seeing as I'm a breeder myself, but my inspiration is for therapy animals. I'm getting more into show Holland Lops, and working extensively with the Vienna gene as well. It is such a rewarding and amazing hobby, but I will warn you there is a lot of work involved.