I know you don't want a reccommendation, but as a comparison look at cihosts.com as I've found it to be the best major hosting provider to compare things against.
However, as for bandwidth. This is definately the hardest part.
First things first though: Storage.
While you can probably guess how much you need, always over-estimate. Then add 25% to that figure at very least.
Another really important factor is to see how much additional space costs. Some providers provide very little space to start but additional space is very cheap, while other hosts do the opposite. So don't just look for the "XXmb of storage space" bit, but look further to see how much adding storage costs. Always plan ahead 😉
Bandwidth is the fun part to figure out. Hah!
Ok, here is what you do. Figure out the most graphically intensive page you have.
Hopefully it's only going to be less than 50kb, but let's say it's just 50kb.
With 3000mb of transfer at 50kb a "hit", you can have 60,000 hits a month.
Note that by "hit" I mean whenever someone actually requests a page from your server (not counting various caching things that tend to happen).
If you have a 5mb file for download you can only have it downloaded 600 times each month, not counting any page hits whatsoever.
Once again, see how much added bandwidth costs. You can also talk to some of them and see if you can work out a special deal of adding only bandwidth to your account for a packaged type deal.
Since some people need only a small amount of storage but a high-amount of bandwidth, many hosts (especially small ones) will be happy to work something out with you.
You usually can't do that with the big ones, however.
Anyway, calculate how many hits you expect a month, increase it by at least 25%, then you know about how much bandwidth you need. NOTE: Be prepared to shell out for twice as much bandwidth as you thought you needed. Plan ahead, but don't shell out money ahead of time for a scenario that might not happen at all.
And a word on anything "unlimited". When they say unlimited, compare it to the size of their company.
A place like CIHosts can back up unlimited bandwidth guarantees pretty easily, however most companies are just blowing smoke.
Hope this info helps you out some.
