You are so lucky!!! I am sure that you will thoroughly enjoy your trip to Niagara Falls. You are also going at a time that is less expensive when the summer tourists have left and hotels are looking for customers.
I am a Canadian citizen and I used to live only an hour from Niagara Falls in a Toronto suburb called Mississauga. I used to go to Niagara Falls fairly often. Here are some suggestions that I have to make your trip more pleasant:
1. Make a bee-line to the Canadian side. Most of the sites and hotels are located there. There is very little to see on the American side and you will find yourself going through the border often. The border crossings can be tedious as it is Canada/USA's busiest crossing. Ques can be excessively long.
2. The temps this time of year can be cool during the day (12 to 20) and quite cold at night (0 to 10). Bring some warm clothing.
3. Sights to see in Niagara Falls: Skyon Tower, Minolta Tower, various casinos, Clifton Hill (great to photograph at night, Marine Land, local winery's (they offer tours and free samples), museums, bird aviary, butterfly aviary, white water rafting (not an exhaustive list). You will not be able to see everything is just 4 days... so pick the ones you want to see and focus on those. This is the official tourism website which will provide you with a comprehensive list of must-see sites and will help you to find a hotel/motel room:
http://www.niagarafallstourism.com/.
4. I would also highly recommend driving to Niagara-on-the-Lake which is just 20 minutes away by car. It is a very picturesque town and you will find much to photograph there. Very beautiful!
5. If budget is a concern, I would recommend booking into a motel about 15 to 20 minutes walk from the falls. There are many of them and at this time of the year, should be reasonably priced. There are also hundreds of restaurants at all price points with foods from all over the world. Please note that there are "authentic" Chinese restaurants as opposed to "North America" Chinese restaurants.
6. Since you only have 4 days, I will not recommend places to see in Toronto (only 1-1/2 hours away). However, if you want to see the "fall colours" which can be spectacular at this time of the year, then I would encourage you to drive 2 hours north towards a small village called Belfountain. Here is the village website:
http://www.belfountain.ca/. The leaves would have fallen by the end of October. Best time to see is between the 1st and 3rd weeks of October.
Sorry to make this so long. Enjoy your trip!