The iPad can serve some people as an excellent laptop replacement, and others not so much. It depends very much on what you do.
There are no Office applications on the iPad with all the features of that you can get on a laptop. However for just writing a letter, there are plenty of options. Here are a couple of reviews by members of the forum.
Compare iWorks, Office 2 HD, Documents to Go, QuickOffice by richsdams
Office Apps comparison (details and examples, very long)
Many members like to use a bluetooth keyboard with their iPad for typing longer emails, documents, whatever. Most bluetooth keyboards will work fine. There are even some cases available that have built in bluetooth keyboards. Browse and search the forum for opinions on most of them.
I don't know what to do for your Blackberry. I'd look in the Blackberry app store (or whatever they call it) to see if you can get a DropBox app for it. If so get a DropBox account (free for a basic account) and the app for the iPad. That way you can move, copy, and download files on both devices. This won't be a solution for everything, but it's a start.
Your company email is a thornier problem. I recommend talking to your IT Staff. If they have external mail set up for POP or IMAP accounts they should be able to tell you how to set it up. If the only allow OWA (Outlook Web Access) then the iPad's ability to use it is dependent on whether they are running the most recent version of the software, and whether they have set it up for mobile access. Up to them, mostly.
There are a few app that promise to improve how OWA works on the iPad. Search for OWA in the App Store and read the reviews. Maybe someone else will chime in with a favorite, but I don't have OWA to experiment with.
Internet Explorer can not be installed on the iPad. There are quite a few other browsers for the iPad that offer extra features, but almost all of them are based on the same engine as the default Safari browser, so they trend to fail with exactly the same pages as Safari does. If Safari is not working for your OWA email, all I can suggest is (as before) talking to your IT people, or trying owe of the OWA apps in the store.
Feel free to ask more questions, but I recommend starting a new thread (in the appropriate forum area) for each one. Individual questions tend to get better responses. I think all of them together tend to intimidate people (or bring out the lazy in some, like me).
And yes, I know we encouraged to you dump them all on us this time. Not your fault, which is why I did my best to cover everything; though I'm sure I missed something.