1. I didn't find it a problem at all, I never had to queue for a shower in the mornings. (I do sciences so I was up for 9ams every day and the showers were always free, not sure what you're doing but it shouldn't make a difference). No one had problems with availability or cleanliness, they're cleaned regularly
2. Honestly, not really, among the student it's very much white middle-class sort of territory, although obviously there are students from other ethnic backgrounds. That might be something you'd have to judge for yourself on the open day?
3. It's about a 10-15 minute walk, into town is downhill, but coming back with an armful of Tesco bags isn't always fun
. You can get the park and ride from Butler (which is about 2 minutes away maximum) but that's like £1.70 a ticket so it's up to you whether it's worth it or not. I got the bus sometimes last year but most of the time I walked.
Don't worry about the open day, everyone's in the same boat so you won't be awkward! Or if you are a bit, you won't be the only one haha. Just relax and have fun, my open day experience was awesome. And feel free to ask any more questions about Mildert/Durham if you've got any