My apologies for a slow response time. My HS graduation was yesterday and I had no time to be online…
To answer your questions…
1) Because Market utilizes custom fields to assign prices, descs, etc, you would not be able to import all of this data because Wordpress would have no way of knowing what goes where. (Although you may be able to get it to work)
2) Same as above, the images are attached to the posts using custom fields, so they have to be specified per post and can't be done all at once :-/
3) You could add a video, but it would require some minor code changes. You also would not be able to use the Market Product Manager to add the video (you would just have to add it in as a regular custom field)
4) There are no limitations. Market is merely a theme for Wordpress. There are no limits on how many posts Wordpress can have, so there are no limits on the amount of items you can list with the MT.