I'm holding Hong Kong Permanent ID & Mainland Travel Permit (回乡证) how long can I stay in China?

Hi,

I am writing to enquire your help concerning my case. I'm from France, and I'm going to study in Nanjing.
I will stop in HK before going to Nanjing.

I have :
- French Nationality (French Passport)
- The Hong Kong Permanent Identity Card
- The Mainland Travel Permit for Hong Kong, as well known as 港澳居民来往内地通行证

I heard that I will have to apply for a long term Resident Permit in the Public Security Bureau (but I have very little information about it, and the procedure seems very boring). Can I NOT apply for this?

If I only use the Mainland Travel Permit, will I have the right to stay longer than 4 months in PRC?

Thanks for your help