Yes, we used the KOA (Canada) many times and recommend it.In July and August it may be crowded, but not in September.
As for the Falls, one day would be sufficient, but for the other natural scenic and historical sites spend more time. A drive down River Rd to Niagara on the Lake, seeing the gorge the river has created.
There are also what I call tourist traps (Clifton Hill, wax museums etc , a Casino, Many people like them, but not me.
Links to consider:
Niagara Falls/Niagara on the Lake tourismWEGO transportationWinery toursMore wineriesWelland Ship CanalHistoric Fort Georgeand these are just on the Canadian side of the border. Lots more on the American side.
Ken