We visited The Falls last summer as part of a trip to Canada there is a link to the trip report in my sig.
Stay on the Canadian side - its far better. You can stay cheaply by using one if the hotels/motels a short walk from The Falls, but I'd recommend a closer one with a view - we used The Marriott Falls View.
In all honesty, there isn't that much to do there, so 4-5 days is perhaps over kill.
Niagara on the Lake (also featured in my report) is worry a visit, and is a short drive away.
The number of vineyards is endless - we only visited one, but you could literally spend a week visiting different ones
Any questions? I'm happy to help