Post crossing guidance.

Hi guys, I'm looking to get into post crossing particularly sending a post card outside of Pakistan. Some of these might seem silly but I need help regarding:

1. what is most reliable and cheap service for it: Pakistan post, TCS, or some other service?

2. where do I get a stamp for the postcard and how much will a stamp cost me if I'm sending the card to Ireland/UK?

3. can I write a part of the message in urdu if it is to be sent internationally? I will be writing the address etc in English of course.

4. do I need an envelope for a postcard?