Vacation in Oman... suggestion please? (Muscat)

I am currently planning to have a vacation in Oman. Was thinking to have a week in Oman. Maybe few days in capital of Muscat and the rest visit outside of Muscat. I saw a lot of attractive beautiful magnificent places in Oman but I really have no idea which place should I really be visited in my 7 or 9 days in Oman. I am open for any suggestion and what would you recommend, renting a car or take public transportation or take a guide with a tour?

How about Islamic law in Oman? DOs and DON'Ts

And how about nightlife in Oman? Where should I go? Just a simply one in the evening should be fine.

Its VoA, is better I pay in USD or OMR for Visa in immigration? Do I able to pay with credit card? Or just cash?

I am grateful for any suggestion

Thank you