My Friend, Congratulation for the New Car. -- Nothing beats the charm/happiness of driving a new ride from Showroom to Home.
Now to your quires, since I got my corolla a year back for this I will like to suggest my experiences for you and the others.
1) If the owner goes ahead an replaces the Euro Star tires with some good ones, will it void the warranty?
1. Not voided if the rim size is same.
2) Which other common actions render the warranty void?
2. Oil other then Toyota's / vehicle wiring modification like adding additional lamps to it without the consent of Dealership
3) Can I drive on Euro Start too or they are just too bad and too unsafe to be on your car?
3. If the drive is within 40 - 50 Km's daily then I will suggest to drive them for initial 2-3 years, if more then 80 - 150 kms daily or alternative day then get them changed.
Euro's are not bad, but the local tire market has better options for us.
4) Any responsibilities such as follow up calls with the dealership, documentation, etc which the owner should take care of or they should just take a nap at home till the delivery call is received?
4. No Nap Scene my friend, always take delivery of new car during the daylight time 11am - 12pm preferred. and check each and every corner and line of body carefully. where ever you feel doubt hold the receiving, until you get fully satisfied with the appearance of the car.
5) Which insurance company for comprehensive insurance is recommended if the owner would like to use Toyota Authorized Dealerships for vehicle maintenance?
I had 2 choices Adamjee and EFU - I picked EFU giving me Falcon-i Tracking system, Falcon-i stands as the best in Pakistan.
Insurance ppl don't recommend to only go at 3S, it your choice, but for the warranty period you will have to stick with 3S.
Even after warranty I will recommend to stay with 3S, yes we pay a lil more then the local market, but it worth killing the element of doubt.