- Mobile version. It doesn't have to be an app, just a website that scales well on smaller displays. There are frameworks that can help you do that (bootstrap for example)
- Fixed width would be terrible. We live in a world where web site can be accessed from all kind of devices, of all sizes. Let the user decide what size is best for him, and scale correctly to that size.
- Do not allow "replies." Replying to a specific post makes the thread hard to follow if the forum is in "flat" mode, which I would guess is what most use. Even worse is that you can't just post a new message in a thread; you have to reply to someone, even when your message is not a response to a specific post.
Also, rather than developing your own forum, you might consider moving to an existing solution like phpBB. It probably does all you want (search, mobile version, compatibility with third party sites and apps...) and more. Migrating your data could be a challenge however.
- Fixed width would be terrible. We live in a world where web site can be accessed from all kind of devices, of all sizes. Let the user decide what size is best for him, and scale correctly to that size.
- Do not allow "replies." Replying to a specific post makes the thread hard to follow if the forum is in "flat" mode, which I would guess is what most use. Even worse is that you can't just post a new message in a thread; you have to reply to someone, even when your message is not a response to a specific post.
Also, rather than developing your own forum, you might consider moving to an existing solution like phpBB. It probably does all you want (search, mobile version, compatibility with third party sites and apps...) and more. Migrating your data could be a challenge however.