Never bluff into more than 2 players. The first hand has 4 players going to the flop. SOMEONE is going to catch a piece of it. The 2nd hand, there's not much point in raising to 500 preflop, 400 will do just as good and risk less with an unmade hand. Bet like 2/3 the pot on the flop and just check/fold it down after that when he calls you. A river bluff might work, but the turn bet is just a waste. Bluffing into hands with a lot of draws is generally a bad idea as well.