I had the exact same thoughts, I don't see anything in David4455's post about leading or guiding a group Some people in these forums assume too much. It seems that the OP has been invited to participate in an art tour. For something like this the minimum anyone should expect is airfare, ground transportation, lodging, meals (this could be a flat per diem rate), touring expenses (i.e. museum entrance fees) etc. Even transportation costs to/from the airport or long-term parking should be included, also trip/medical insurace while on the trip. This goes for your partner too, if he/she was also invited. In the original post, he was only expecting lodging & meals.

Anything above this should be negotiated, like upgrades. The agency might be able to arrange this with the airline depending on the relationship between them. However, in my experience (in California), a "high-end" agency may not necessarily be a "high-volume" agency, the airlines seem to do more favors for the latter these days.

"We aren't that famous but we do have a name recognition in our field. We have never been on an organized tour before."

If you've never done this before, then don't go too overboard in your requests. Also, might the type of participants you'd meet on the tour be beneficial to your profession, making you more famous? Provided you have no objection to that of course.

If you do the tour and later find out that you like doing this type of travelling, then you can negotiate for more on future requests of this sort.