The maximum Health level is 99. You will need to collect the greenish blue gems that enemies drop in order to upgrade it. This will come in time, though slower than Blood, and will most likely be in the very later half of your third play through. Alternatively, for $1,000,000 for a set of 100, you will be able to purchase your upgrades if you get tired of grinding.
Money Grinding Method:
The easiest method (that I've found thus far) of accumulating money quickly is to set the game to Nightmare Mode and replay Episode 1. The Episode is 35-38 seconds long and will reward you with anywhere from $720,000-$729,000 money per play through on Nightmare Mode. REMEMBER TO UNEQUIP THE DARK BOOSTER AND ULTI-MONDO COSTUMES WHEN MONEY GRINDING.