try the pump you have.i would use at least a 3/4 or 1 in. diameter hose from the pump to the waterfall if you use too small hose, you will loose too much water pressure.

I am by nature cheap too. I am also the guy who claims that my stream solves all problems. Your pump is a little small but still useable. In the future, it would be wise to find a magnetic drive pump. They are less expensive to run and the extra expense will be saved over a year's time. However, it is too late for that now. Your stream will work with almost any flow rate as long as it falls gently and little puddles or ponds are formed. The critical issue is to have plants in the stream for filtering.

If you can find/scrounge a second in pond pump, you can just increase the flow by connecting it in line with a tee or y fitting.

Buy the dirty water submersible pump by chicago sold at Harbor freight, they usually have them on sale for $30 it's 1 1/2 horsepower and pumps about 1650 gallons an hour. It has a strong flow and will do better for you if you're pumping uphill. Plus they guarantee them for 1-2 years if you buy the warranty. They usually last about 1 1/2 years.

Here is a link that might be useful: Gabelmans Gardens blog