The number of hits of Squall's Renzokuken is indeed based upon his Crisis Level. This number is based on your current HP compared to your max HP, any status effects currently being suffered from, how many allies are still alive (one or more KO'ed will increase it), and whether or not you are in Aura status. The higher the crisis level, the more hits Renzokuken will have. There is also an element of chance involved, so whilst having a high crisis level will increase the chance of more hits, it isn't a given.

As for finishing moves (because someone is bound to mention this), they each have a set chance of being picked. A higher Luck or increased crisis level will NOT increase the chance of Lionheart being picked, although a higher crisis level does increase the chance that a finishing move will occur. So for the sake of arguement, yes a higher crisis level does increase the chance of Lionheart occuring, but not directly.