#1
Here's a question. How many bars do you usually have in an entire hardcore punk song? Should this even matter to know?
#2
As many as you want? I don't know, I played in a hardcore punk band for about two years and we never considered that.
Telecaster - SG - Jaguar
Princeton Reverb, Extra Reverb
P-Bass - Mustang Bass
Apogee Duet 2 - Ableton Suite
#3
Follow your heart. You can make a song as short or long as you want. Typically, the average song length nowadays is 4-5 minutes so thats the typical rule of thumb for length of song. Of course, break the rules, write a 45 minute hardcore punk rock opera song.
Derpy Derp Derp Herp Derp
#4
^ The Decline! Best punk rock album/song ever!
Telecaster - SG - Jaguar
Princeton Reverb, Extra Reverb
P-Bass - Mustang Bass
Apogee Duet 2 - Ableton Suite
#5
There is a difference between 100 bars at 130bpm and 100 bars at 90bpm.

Its song length you should be asking about. Anywhere between 2 to 4 minutes would probably do for a punk song, but it's subjective.