Q. What does the "P" in the 5P of the Predator mean?

yep, P is Physical.

Q. So, how much base damageboxes does a 5P Predator with AP -1 to a 6/4 lined coat ? zero ?

The coat would add 5 (not 6) dice to the resistance roll.
Base damage would be the DV + net hits on attack test, minus hits on resistance test.

Q. Is the -1 AP modifier only for checking for stun or physical damage?

It's also for reducing the Armor dice. The 6 ballistic armor on the lined coat becomes 5 bonus dice instead of 6 for the defender.


Q. How are shot rounds for shotguns treated?

They have 3 different spreads, narrow, medium, and wide. They can shoot only 1, 2, or 3 targets within a meter of each other respectively. Damage code gets modified for each, defense roll gets different modifier for each, harder to dodge wider spread.

Q. How do those "super extra wide bursts" affect the power of shots? It seems like shotguns are still as stupid as ever.

There are Narrow and Wide bursts and autofire. Narrow increases damage, wide increases likelyhood to hit. With shotguns there are basically 3 choke settings that allow you to hit more targets, and/or make it harder to dodge and decrease the power of the attack.