Get a DropBox account, and install the app on your PC and the iPad. You'll be able to synchronize folders full of files with this account. Easy.
Uploading raw files to the cloud can take a really long time, depending on your connection speed. You can do this, but I suspect you'll be unhappy with the time it takes.
If your web site uses Flash, an iPad will not display it at all.
A wi-fi connection works anywhere there is a wi-fi router nearby. Perhaps you are asking about a cellular connection? If so, then it depends on the location of the tower. (And btw that's even slower to upload raw files.)
I think the "cloud" is great for small things, like delivering photos to clients or keeping a portfolio or some files handy. I use Dropbox every day. But it's not my primary means of storage and likely never will be.
An iPad is a fun device, but I found it easier to deal with if I did NOT treat it like a tiny computer. It's not -- it's more like a giant phone, or a souped-up e-reader. I can show my portfolio (using the Portfolio for iPad app, and syncing the folders with Dropbox, natch), check email, browse the web, watch movies, play games, etc. With Filterstorm Pro, I can download photos to my iPad, tweak them, caption them, and then transmit them to an editor using email or Dropbox or FTP. But it's nowhere near as easy to do this as with a small laptop.
Have fun figuring out what you can do with it.