No, your visa validity will be only for 30 days from the date of issue. You have to utilize your visa before the visa validity expires. So, you can apply for your Oman tourist visa a month prior to your trip at the maximum.

Yes, you will have to enter both your living country and citizenship country while applying for your Oman visa.

No, citizens of Somalia are required to have their Oman visa when traveling to Oman.