Hi there!
I've just completed my gold and silver dofe and I intend to do gold next year
1. I'd recommend local charity shops, libraries, maybe at clubs in your school. Staff are generally friendly in these kind of places so just ask around. I did mine both times in the same charity shop
2. Your meant to do like an hour a week but I didn't do it some weeks and other weeks I'd do 2-3 hours so overall it was approximately 6 months. It is quite flexible, however if your not able to commit to doing 6 months worth of work then I don't think silver or gold are for you as it's quite time consuming
3. Yes, I did my expedition before other sections and it was absolutely fine. Just make sure you get it all signed off afterwards
4. Bronze: 3,3,6 months
Silver: 6,6,3 months
Pretty sure gold is 12,6,6 months
Hope this helps x