Welcome back, and sorry to hear about your wife :(
As for where to go with things on the site.
1. I would definitely look at upgrading DotNetNuke, you definitely want to do this locally first though to test things out. All of my sites are running on 5.6.1 now
2. Backup, backup, backup, for sure you need to do this before doing anything else.
3. Forum module, I heavily encourage use of the core forum module now, I have it running at
http://www.sccaforums.com, though conversion will be an issue, you would likely need to write some custom conversion scripts for this. I have some scripts that I've posted and am blogging about converting from CommunityServer to DNN, they could probably be tweaked a bit for YAF
4. Store, I can't help you there, been a long time since I've done anything with e-commerce.