Also, in my view, you are going at the wrong time.Dudhsagar is best during monsoon. July August preferbly. This is when it is full bloom. Water gushing at its mercy.

i think yes you can walk......... but if you want to walk there is nice jungle road trek that is much more enjoyable it takes around 4/5 hrs one way

Try carrying food & water for self for sure. if you are reaching on weekend, there is a snack corner close to the dudhsagar bridge. if you are reaching early in the morning in kulem, there will be no one. in the morning after 06:30 am you can get food outside kulem station and everything is available. easy way is to catch the jeep and travel. adventerous way will be to walk on railway track and reach dudh sagar. there is another option you can drop at castle rock station and plan your journey next.

If you are travelling with Family of 4-5 people, will suggest you can take small kids. It will be raining heavily during monsoon time. have seem individuals getting small kids with them and later struggling to handle them and individual exhaustion.

Yes. It will be available

During March, South Goa will be deserted. Also, there will be more varieties (beaches / activities) in North side. So, it is better to spend more time in North.