Hi James,
I am a 34 year old female and traveled all around Europe solo and I find that staying in hostels is one of the best places to meet people. I researched the hostels alot before I left as I wanted to make sure that I wouldn't be staying in a party hostel. My favorite ones were a little more expensive than the rest (but not by much). I liked it when they had a bar or lounge as they were great to meet other travelers. I was surprised how many other solo travlers are out there and that we would instantly hook up and hang out together. Usually the ones in groups stay together and keep to themselves.
Sign up for city tours. I went on many "free" tours that were great to meet other people. You pay a tip at the end and it still works out to be pretty cheap.
I usually ate at the pubs or had street food. Street food is great if your by yourself as you can eat on a park bench and people watch. Making sandwiches back at your hostel is good as well and you can eat at the parks.
I wouldn't worry about safety at all. Just use common sense. It's safer there than at home. Bring a lock for the hostel lockers. You might find more theft at the hostel than on the street. I brought a cable lock to lock my bag to the overhead rack on trains, so when I went to the bathroom I didn't worry about my bags...never used it.
Reserve ahead now for Queen's Day. It will be busy!
All you have to do at hostels to meet people is ask the same required questions off the hop-"where are you from". "how long are you traveling", "where have you been", "where are you going". After awhile you will be sick answering/asking these, but hearing other peoples stories you will wish you were traveling for a few more months!