The Single Page website
The advantage of having just one page is that all the information is presented to the visitor without them having to load a new page.
There are other considerations relating to the choice of going with a single page, these include the impact on SEO and the ability for you to able to track the sites performance. The Friends Project started with just a single page and could well stay that way.
The Friends site is primarily designed to promote a limited range of information. This information, such as events, can be linked to the single page as pdfs.
Multiple Pages
This is what I have on tempusfugit, in spades. There is just too much information over a wide range of topics to not have multiple pages. Also the tracking and SEO would not work in the same way.
Coding a single page site
The coding is the easy bit, the hosting and admin is what you will need to know.
a Few pages
I think that this may be the best compromise for the Friends website. I can link the membership sign-up PDF but the donation form (if it is decided that what is wanted) is better on a seperate page.