Treat this like some kind of minor install. What sort of connection are these 100 devices expecting ? What applications are they intending to use ? Will they all be requesting data at the same time ? Most any AP will allow you to adjust the maximum connected device count and (I believe) they will all default to 100 anyways. If the expectation is simple, almost any indoor/outdoor AP will meet your requirement.
At the very least, I guess you would want a dual band AP. If the area is large enough, get something with either space to add an antennae or look at something like the zf7982, it gives good additional gain built in.