Is the river going to be high in may due to flooding.

It's always possible but depends on weather at that time. Usually not a problem.

Probably not. The river is prone to fast rising and falling due to heavy rain. There is an app called riverflows.net that gives near real time river information that will keep you informed. May is usually a great time to go.

Flooding is always possible during heavy rain fall. But generally the river is good to fish. The river starts in the park due to the spring. So its a spring fed river. In may the river is usually good accessible but may vary due to weather conditions. I personally never had any problems in that time.