Hello Kate
I have been on a Eurostar tour I did the France/Belgium Battlefields tour..
No it is not far at all the walk from Euston to St. Pancras
The train journey is just like a normal train journey, you are responsible for getting your case on and off the other end..you are allocated a seat number the group were near one another..the couple of people who upgraded said it wasn't worth it. For me I was happy in the normal seating, just get a few nibbles before you leave home to eat on the train, as you get ripped off at the main stations.
The battlefields tour was very constructed and did not leave much free time, but I like that.
If you have a date in mind try asking Monty on the editors board how many and male female ratio age that sort of thing, she should be able to give you an idea.
The European tours I have done seem to be smaller groups 15-20 than the large USA ones up to 40 people.
Any other questions just ask..
Cindy