I am going to start over six companies. One company will import products from other countries and there will be different websites with different names devoted to the different types of products (All of these will be online stores). Also, there will be three or four different websites that will contain information about business start-ups, video uploads, etc. Should I go with a reseller account? Why is there such a difference between the disk and bandwidth space between shared hosting and reseller hosting? Also, how much space do you think I will need to host all of these? I am not sure how much disk space and bandwidth I need. Thanks a lot.

What hosts do is "oversell" shared hosting. So you normally do not actually have the total amount of bandwidth that they say you have. Reseller hosting is shared also, which basically means you will be paying for the same hosting server space as on a regular shared hosting package, but you will have the ability to resell the space you don’t use. Many use this feature to host several of their own sites, as you want to do. Most sites do not use anything near the bandwidth they are offered.
The average web site contains a mix of text and images throughout its pages, and may or may not offer files for download. The average web site also gets average traffic, meaning anywhere from 50-500 visitors per day. Assuming these factors, a hosting plan with anywhere from 3-5 gigabytes (GB) of data transfer per month should suffice. (See why i say most sites never touch their bandwidth limit) For sites that get more than 500 visitors per day, or those that offer numerous large files for download, it is wise to secure a hosting plan with 50 gigabytes of data transfer per month – or more, which is not hard to come by these days. It is important to note that most web hosts quote your allotted bandwidth in "per month" terms, when in fact that number is actually broken down to a "per day" limit. So you want to stay away of these factors as they are closely monitored by all web hosts.
I think You need only 60gb.
The Silver Package in Reseller Hosting would be quite enough.
http://www.hostgator.com/resellers.shtml
The Swamp in Shared Packages looks nice too.
Although it has extremely good features. But what will you do with 1TB?
I prefer Silver Package of Reseller Hosting..
So Choose Wisely.
http://www.hostgator.com/shared.shtml