To maximize your revenue, you should consider multiple payment sources. PayPal is one choice you should allow to your users. Some people don't want to use PayPal, but are willing to use their credit cards online in a secure (https) environment. For these people, you can use a credit card billing provider like Authorize.Net. Finally, some people don't want to do any financial transactions over the internet, so you still need to give them the option of printing out the form and mailing it in with a check. If you cover these three bases, you'll get the most revenue out of your users.
As far as creating the forms online, this is more HTML on the front end. Once you hit "Submit", that's when you are going to use the bulk of your PHP/MySQL experience. One thing that is nice, is you can use PHP to pull variables into an HTML document, like dates, from an external source. So, instead of changing 20 documents every year, you simply update the external source. While the setup for this is a lot of work, the maintenance afterwards will be incredibly easy.
For an easy start into HTML, you may want to try a book called something like "Teach Yourself HTML Visually". It's a book that's easy to follow and get up to speed quickly with.
