Interesting post because a friend of mine basically does just that.
1, You need two planes min, must be high wing, sightseeing is the draw, say a C180, carries four passengers (plus pilot), and say a Beaver, carries 6 or 7 plus pilot. Get both kitted with sightseeing windows etc. (That way you fly parties of 3/4, 5/7, 10/11 in the most efficient way possible.
2. Need a tame tourist business, coach tours of mature tourists etc. Sorry, you have to give considerable discounts and commissions. Inducement to the agents and a further reason for the tourists to book. Typical cost around here is $80 plus US for 25 mins, discounted to about $50 net for most of the passengers. Walk ins etc are the bonus, they won't keep you in business in a hundred years.
3. Allow for typically 100 hrs/plane/month busy season, less for shoulder. If business is poor, Like now after 9/11, you might fly as little as 60 hrs/mo high season. Weather can block out whole periods, you have to allow for it.
In case you think, "that's not much, we'd do more than that.' 60 hrs/mo is four flights a day, 7 days week. Some days you might do 5 or 6 if you are really busy, but some days you will do one, some days none. (and that is per plane after 15 years of making friends, customers and contacts in a very busy resort town.)
4. New insurace wrinkle. Insurance companies who used to insure for 'seasons' and offer 'non moving only' for remainder of year are now insisting on full annual insurance, just about doubles insurance rate, which in itself went up about 40% in last two years.
5. Also got to allow for hundred hour checks etc. If you are not right on a service facility you not only lose flying time but you also have ferry cost.
Still think you can do it?