1. No
2. Yes, Immigration might ask few questions. Please inform them that you get visa on arrival and relative is staying in Qatar.
3. No.
4. No need, just mail copy of your QID and your local address.
5. Yes, its free.

My father came last week.

Only three things you need :
1. Passport validity shall be more than 6 months
2. Confirm return ticket.
3.Local address during stay.