When do the bands start for the day, and when do they stop for the night? I am planning on going eventually.

Also, are there plenty of English speakers at beer and food stands?

Sorry about this post. I have posted here before about Wacken and forgot about these questions

The level of English understood and spoken by staff at Wacken is varying. But to order food and beer you don't really need much in the way of verbal communication, so you'd be fine regardless even if you speak no German at all.

I can't recall when music starts, but it's fairly early in the day iirc. Maybe already at 12?
Generally I think the last acts go on at like 01.00 in the morning.

You can look up running times from previous years to get an idea of this sort of thing. Wacken has lots of stages and other non-band events/activities, but it looks like around 11am is when the music starts.