I say it is too big because of a concept called Dunbar's number. Basically humans can only have social connections with about 148 people. When the first congress met there were 59 members. When the current sitting one hundred and eleventh congress first met, there were 434 members.
I'm not sure how to solve this problem. Perhaps we can draw up congressional districts without regards for state lines, and have the state legislatures appoint senators. The lower house can be reduced to about 125 members, which will account for the local office, and non elected people in the capitol building the congressmen will have to interact with regularly.
I don't pretend to have a clear answer to this problem, I just know that 400+ is to many people.