Just like to know if I need to tune after replacement and if yes, can I drive the car to the garage to do these.

There is no moisture in the skylight area, nor the front or side windows. Only lots of water in the foot wells

Is it easy to replace yourself?

the battery light also came on in red.
I stop the engine and restarted the car and all appeared fine.
the next day it happened again this time all the warning messages appeared then eventually the car shut down and would not restart. totally 'dead'
could it be battery or alternator?

At what intervals I should replace it?