The NEC does not specify any limits on the number of outlet on a circuit. It can be as many as you want. Some AHJ does limit the number of outlets that you can have, you would have to check with them in your area. Although there can be issues, such as derating of wire, etc. which we won't go into here. Using the formula watts(power) = I(current) X E(voltage), you get max 1800 watts, therefore, you can have 18 100 watts bulbs, 30 60 watts bulb and so on. This assumes only resistance load( light bulbs, some heater, etc. HTH

PS. it is $:00 in the morning here and my thinking might not be to clear. (:>)

Let us know how it works out.

In the strictest sense of the code, a barn is not a dwelling, so you would be limited to 8 outlets (receptacle or light) on a 15A circuit. Your local inspector will be the final authority.