Keep in mind that the trunk in a limo is really no bigger than the trunk in a towncar.
On our 14 day cruise/WDW trip last year, we had a lot of luggage.
Four large suitcases, a garment bag, a smaller "roll-on" suitcase, and three totes. The luggage did NOT all fit into the trunk, one of the larger suitcases had to ride up front with the driver.
Also, there really isn't that much floor space in a limo, and frankly if you're going to be using car seats, getting the in and out is very awkward. You might be better off getting a van--more cargo room and much easier to deal with getting in and out of.
Anne