Efficiency of score checking

So this is basically what I've got. The function runs every 20 ticks so every 20 ticks there is a roll for the chance to spawn and then another roll for the type of mob.
The potential problem is that I'll need a summon command for a large variety of mobs so it will be a lot of score checking (want to have the chance to summon almost any mob). 
So, I was wondering before I write out all the commands, if this way of checking the two scores is very good. And if there were say 100 spawn commands would that be a big strain on the game?