Engine System Fault Plus Other Issues

I have a automatic 2006 ford focus ghia 1.6.
Sometimes the engine wont start unless the ignition is turned numerous time and almost every symbol comes up on the screen or I just sit and wait and I see the "P" on screen and then it starts ok. At other times it works fine first time.

Also, while driving, the speedometer sometimes doesnt work, and messages such as reduced acceleration and engine system fault shows up along with all the symbols such as 'abs', 'immobiliser light', 'engine oil', 'airbag' etc. And the car jerks a little and then again at times these go away.

I took it to a garage and they said the ECU board was damaged and water has got into it. Can this affect the starting of the car? And will replacing the ECU fix the problem?

Many thanks for any advice given.