Visa requirements for a Portugal citizen living in Czech Republic

Dear Sir/Madam,
I am planning to visit China in March 2016 and I have some doubts about the Visa Requirements:
1. Is it possible to take a Multi-entrance Tourist L type? Reason: I'm visiting South Korea and Mongolia.
2. Invitation letter can be obtained by a friend living in PRC?
3. I am from Portugal and live in the Czech Republic. Is the work contract enough to provide the reason why I am applying for the entry permit in the Czech Republic?
4. Is it mandatory to have the flights already booked before applying for the L type?
I am looking forward to hear from you soon.