Visitor featuresWhat should the visitors be able to do on this website? What kind of user interactions will the site have? Most importantly answer why. This should all be defined based on a content strategy / information strategy etc. What about multi-language support on content and the editor interface? What about features such as: contacts, events, press releases, product catalogue, webshop, automatic creation of PDF's such as reports, image gallery, videos, FAQ, user comments, forum, blog, wiki. Will there be specific needs concerning advanced content and design such as storytelling, copywriting, art direction etc.
Administration featuresHow will the website content be updated? Will there be any particular process for adding and modifying content? How many persons will be doing it, how often? How computer literate is this person who will be updating the content? Will you need to manage an online community associated with the website? In that case you might need a community manager, moderator etc.
Future site upgradesIs it important that future developments to the site can be done by most development shops/consultants? If so state a requirement to use a commonly known CMS. Do we need any service level agreements for system changes to the site? Do we need support for the content editors? Do we need technical documentation on how the site is built? If there is a lot of advanced customization this might be a good idea.
ScalabilityIs it highly likely that the site will become very popular within a few years? If so consider SaaS, PaaS, cloud services etc. to help you cope with dynamic traffic demands. This is also relevant if you know the site will have extreme traffic spikes at specific times of the year.
Site structure and contentCreate a hierarchical view of the pages that will be part of the site. This can simply be a document with level headings going from heading 1 to 4. You probably also want to provide multiple ways to your content by using tags or categories? Will there be user generated content and what is the extent? Will there be massive amounts of content? What is your unique selling proposition (USP)? How will your site stand out?
Logging and audit trailIs it important to log things like who did what when with site content?
Key Performance IndicatorsWill the persons responsible for the website be followed up on KPI's? E.g. maybe the web team is required to create a new post each week? or maybe there is a requirement that the site should have a certain number of visitors or be on a list of top sites within a specific category?
Visitor tracking and reportingYou probably need to visitor statistics. Is Google Analytics fine?
Search Engine Optimization (SEO)How high are our ambitions when it comes to being found on and ranked high on search engines?
AccessibilityShould people with special needs be able to use the site? How much support should they get? Should they just be able to read it or should you provide good user experience for this group? Should blind people be able to use the site?
Where should the site be available? What kind of devices? Old devices/browsers?
StyleWhat kind of look, mood, style do we want? How do want to be perceived? Our values and mission has to fit the style. What level of design excellence should we strive for? Is it important that the readers find the site really good looking and appealing?
SecurityDo we need special considerations when it comes to security and permission control? Will different people need different access to some content? Will some editors need more permissions than others?
Is it extremely important that the site is not hacked? Hackers typically break site and put advertising and malware on hacked websites.