New to Riyadh

Please help me with below queries
1. When coming to Riyadh , do we need to register with embassy after landing.What are precautionary steps need to take before and after coming to Riyadh

2.Which is best area or compound (as I learnt) to stay where it is more modern and safe.

3.What is average rent .

4.How do people generally commute to work.What is average expense on travelling.