Here is site that covers a lot of differences. http://www.13thman.com/cflvsnfl.html
Specifically to penalties is the Fair catch (NFL) vs. No Yards rule (CFL) on kick returns, but in general some of the bigger differences include:
Field length and upright position
Number of players on the field
Number of downs
Scoring rules on kicking plays
Fair catch (NFL) ...
The game as a whole is made simpler and more coherent if it is only possible to move forward when attacking, and this requires that it not be possible to move forward when defending. To be attacking, a team must have possession, one way or another. The exception is backward movement made as part of the attack, i.e. the snap and any backward passes or runs: ...
A spike is indeed typically assigned to the "team". For example, you can review the play by play of the 9/23/17 game between Kentucky and Florida, and you'll see at 0:21 left in the 4th quarter this play:
1st and 10 at FLA 35
(0:21 - 4th) TEAM pass incomplete
In NFL statistics, they simply reflect the play as "... spiked the ball", and ...
The rationale here is that when the defense stops the ball carrier, it is preferable that they do not get any benefit from holding the carrier up (so the play would remain live) and just pushing them backward a huge distance instead of tackling.
This concept is in the rule book as "forward progress"
SECTION 13 FORWARD PROGRESS
ARTICLE 1. FORWARD ...
It is specifically covered in the NFL rules for 2017 as rule 12, section 3, article 2
the defense shall not commit successive or repeated fouls to prevent a score.
Penalty: For successive or repeated fouls to prevent a score: If the violation is repeated after a warning, the score involved is awarded to the offensive team.
In the same section, article 4 ...
In the scenario you mentioned where it is currently 2nd & 4 any penalty that advances the ball 4 or more yards will result in a first down. This happens because the offense just has to get the ball to a certain yard mark for the first down and it doesn’t matter if they get it through plays or penalties.
As for the second part of a question when the ...
According to wikipedia all yardage penalties are
capped at half the distance to the offending team's goal line.
Thus, the new line of scrimmage will be the defensive team's 6 yard line.
NFL: 2017 nfl rulebook rule 14 penalty-enforcement
CFL: summary of penalties
NCAA: 2017 football rules