Kathy, Welcome to the exciting and fascinating world of beekeeping. I assume that since your friend is a beekeeper, he will do the actual working of the hives. It's exactly the way I got my start and I'll have 11 or 12 hives this year. First off, go to your local library and take out a book on beekeeping. You'll probably want to buy a veil so you can help out or at least get up close for a good view. Don't be afraid to ask your friend questions or voice any concerns. After all, this will only work if you are comfortable with the arrangement. My only warning is you may also get hooked.
your questions:
1. How close you can mow depends on the temperment of the bees and the set-up of the hives. You don't want to be directly in the flight path or be throwing grass at the entrance. If needed, some shrubs or a section of fence will make the bees fly "up" as they leave the hives. I usually just pull up anything that is directly in front of my hives by hand.
2: Basically, a swarm is the bees way of starting a new colony. The queen leaves with about half the colony after new queen cells are established to replace her. A new swarm is usually one of the most gentlest group of bees. They are full of honey and looking for a new home and are not likely to bother anyone. The movies make them look scary but it's nothing to fear. A hive won't "swarm" you.
Africanized bees are a different story.
3: The bees will go about their business and it's a fascinating business to say the least. I love to sit beside my hives with a cup of tea or coffee and just watch and listen. You'll see new field bees taking orientation flights, bees coming in with pollen, propolis, nectar and water. I love to watch the guard bees check the field bees as they come back to the hive. House bees take out dead bees and other trash and drop it away from the hive. Then there's the great hum of a busy hive. That's just some of what you'll see and hear from the outside! Inside, it's an amazing world you won't want to miss.

Hey Tonybeeguy:
Thanks for the great info. Yes, my friend will do all the beekeeping - I just get some free honey :) He has about 17 hives in various friends yards, so I have no worries that he knows what he is doing. I hadn't thought I would get involved at all, but I may get a veil when I get a little more comfortable with it all just to check it out. You have made it all sound exciting - it's funny that my friend says he loves to sit in a lawn chair and watch his hives work too!
And...you have helped me make my decision to do some planting around the hive so I don't have to get too close with the mower. I think that will be better all around - and it will give them more to pollinate. I better get started because they are coming in about two weeks or less.
I'll get some books on this tomorrow - great idea!
Thanks again!
Kathy