Typically a good rate on a minivan is around 199.00 a week + tax. If it is any lower then you are doing pretty good. One thing to remember, if you rent from Dollar, lately they have been giving regular wheelbase Caravans and charging an upgrade price if you want an extended wheelbase model. They don't do this for everyone, it seems to be hit or miss. But the regular wheelbase models have a lot less cargo space when all 7 seats are being used, just one more thing to consider.
In regard to your last question, it really depends on how much luggage you are bringing for the seven people and what you mean by comfortably. You may have to put some luggage by the passengers feet etc., depending on how much you bring, so your drive to your hotel may not be the best, but once you drop the bags off 7 people fit pretty good in most minivans, some of the minivans even have seats for 8.