1.Normally the date you join the company is considered for annual holidays. For example if your DOJ is Oct 15 then every year Oct 15 will contractually make you eligible for 30 days paid off.
2.Yes he is but as a professional and team player you should get prior approval from your boss.
3.Yes it is. One year is 365 days. As per Qatari Labour law they will give you an extra 3 days basic.
4.We cant say its legal or not , it your company policy.