Re: Upgrade/backup/large site size questions
You shoudl back it all up, yes. But you don’t necessarily need to ftp it down to your computer. I normally make a copy of the folder right on the server.
If you are double-sure you have cache files, you can clean them out. What are you using the cache? Because wp-super-cache has a cleanout button back there on the admin screen.
It’s not unusually large, no, dpeending on how may users and/or visitors you have. Lots of users, lots of hits, means lots of cache files & loads of upload files if they like to post pics to their blogs like you’re Flickr. (Hi mom!)
Yes, you’ll want to backup the db as well. Optimize those tables, and if you’re really feeling frisky, clean out the spam.
Remember that with the BP upgrade, the theme changes location. The MU part should be smoother.
Pick a time when your site traffic is low, like the weekend.