I want to brew, or average, twice a month. This month, I'm brewing three times. I have enough empty kegs for two batches right now, but have one batch that will go to keg this week (started on the 10/6, so it's good to go to keg anytime this week). I brewed a batch yesterday, which will go to keg early next month. The batch I'm brewing this coming Saturday will be several months in process (a BIG barley wine) so I'm ok there. I do have the kegs it will go into already set aside (a pair of 2.5 gallon kegs).
Over the past year, or so, I've been brewing about once a month. This was due to not being able to brew at home, so having to go to a friend's place to brew. We would both brew batches, so it was more based on his availability and such. Not much of an issue, just had to be sure to pace myself better. Now that I have a place where I can brew freely, I'm planning to do so. There could be times when I brew every weekend, or go a month (or more) between batches.
BTW, I aim to hit the 100 gallon mark this year, or come damned close to it. I was able to get there the first full year I brewed, so it's more a personal goal. Next year, I should easily hit that mark.