Creating new material for the Web site instead of repurposing existing material is a costly proposition. It may be the best route but repurposing should be considered first. If you have existing text documents to move to the Web, consider how many Web pages they will be. So think about the size of your pages in terms of how long it will take to download. If you're putting a 300 KByte product manual on your Web site, estimate it as being ten 30 KByte pages plus one more page that links to each of the ten sections.
Graphics greatly enhance the appearance and sometimes the usability of Web sites.
The problem with graphics is that they tend to eat up download time. You may have a collection of graphics available from print ads and product brochures. Maybe you can use them, maybe not. Large photographic images can end up being image files that take minutes to download. That includes graphics, too.