If you are large enterprise and run a busy forum you will need a lot of hosting space, but if your web traffic is limited then you can go for modest storage. However, to be on the safe side, plan out an average of 30KB/page which will let you sail smoothly with even 10MB of space.

Bandwidth is the data volume that your web host allows you to transfer monthly and you pay for it. All types of uploads and downloads, no matter which protocol is being used – HTTP, FTP, POP etc. bandwidth is dependent a lot on the average size of the page, but it is affected by the traffic that gets directed to your website. How many pages are visited on an average is also an indicator of bandwidth requirements. For your 30KB page size, 20,000 viewers monthly and 3 pages per visitor, you will require around 1800MB (1.8 GB) of bandwidth monthly. This much is easily available at affordable rates. In actual, 20,000 visitors is a cherished dream for many websites, usually visits don’t exceed 2,000 per month.

It is safe to assume that if you are not offering heavy downloads and monetary transactions are also not heavy then you don’t need to buy higher bandwidth.