1. You can have as many battles as you want as long as you Card the enemies to prevent you receiving EXP.
2. Omega Weapon and the monsters on the ICTH/H are always Lv100 regardless of your party level, so they do pose a larger problem than most other enemies.
3. The monster's level is 80-120% of the average of the three characters in your current party. Characters not in the party aren't counted.

Quote Originally Posted by shinangel2292
it'll be harder finding some rare items which are only dropped by high level enemies
Use Tonberry's LV Up ability. Lv30 and above qualifies as 'high level'.