L visa: is an invitation letter enough (no return flights or hotel bookings?)? What does it contain?

Thanks for your help.

I am now in Shenzhen,
I have a normal Belgian passport, and
my current L (30 days, 1 entry) expires on 24 July.

The new rules state that I can only get 1 extension of 30 days inside, but I need more time (at the time I got my current L you could extend 2 times).

1. Can I get an L (tourist) in Hongkong without showing any hotel bookings or flight tickets (in and out of China) when I go myself to the PRC consulate to apply?

2. is this possible with an invitation letter from an individual i.e. a Chinese citizen resident in Shenzhen?
(there are no flights from Hongkong to Shenzhen) Do I still need to show a flight ticket out?

3. what is the content (text) of such an invitation letter from an individual,
which (copies of) documents (passport and/or ID, house registration, income slips ...？) of my host have to be included,
do I have to sign this letter or include any text or (copies of) documents from my side,
does this letter have to be stamped or signed by any officials (if so, which officials?) in Shenzhen and
how long does that take and cost?

4. if I re-enter PRC immediately after getting the new L, should I apply for a 1 month L (1 entry) or a 3 months' L (1 entry) because I understand (rightly?) that even a 3 months L is only good for 30 days' stay (which can be extended only once for 30 days) or can one stay longer (up to 90 days?) with a 3 months' L and how is that possible under the new rules?

Sorry for the great number of questions, but many others may benefit from reading the detailed replies.