Seconding what the first poster said - I actually played 3 on Normal and even then I had to learn to cheese the bosses way more than in the other games. Grab the boss, kick them on the floor, repeat till you can carry out a Heat Move. If you can't grab them then try to get behind them and get an attack or two in. Iirc weapons are pretty useful in this game, especially if its tough to use a Heat Action otherwise. The weapon dealer guy has shops in both Okinawa and Kamurocho.
When it comes to making money, iirc the best way other than gambling is the Hitman missions. There's cheat items for gambling in this game so that's also a great way of making a lot fast. For more info take a look at CyricZ's excellent as usual guide.