You have to go out of Maldives, and send a letter to the immigration, mentioning your intention and re-enter.
No, your intention to get married to a Maldivian should be submitted in writing to Immigration before your arrival in Maldives. (A fax to 960-321100 would do).
Make sure that you receive a copy of the Work Permit, issued by the Ministry of Employment and Labour, from your employer before you leave your home country.
No, a tourist will not be switched to a Work Visa to work. Work Visa is issued to expatriates who enter Maldives with a Employment Approval (EA).
Normally on a single entry, you can stay up to 90 days. This is subject to conditions, read the relevant section.
You have to submit a Visa Extension form to the Immigration Head Office before the expiry of your current visa. Again you might have to prove your financial status for the duration of stay.
No, you will be granted a free entry visa on arrival. Depending on your financial status, you can apply for maximum thirty days.