The way I see this, you need to have a reasonable number of people in a committee so that everybody knows each other and can hold a meaningful discussion, i.e. without necessarily working through the Robert's Rules of Order or its local equivalent. I've see research stating that the max number is seven, but we don't need every decision to be taken in a single day either. A dozen people seems right to me.
12 committees with 12 members each should be enough to address meaningfully the pertinent legislative questions, or ~150 people. This is not exact science, of course.
Yes, but it's harder to secretly bribe a large number of people with small sums of money than a few people with a large sum of money.
In other words, the more people there are, the more likely at least one of them will be honest, and even more so if the gravy is spread thin.
In a country of, say, 300,000,000 people, it is easy to bribe 150 politicians. Having a total legislature of 150 people in a country of that size would be quite easy to manipulate, and constituencies would be huge, meaning politicians would have no real ability to connect to their constituents.
