Don't worry too much about RAM usage, and don't use task killers. Unlike with Windows or your usual linux distribution, android has control on which app stays in memory and which one is killed. And it is pretty good at managing this without user intervention.
As for battery life, I recommend BetterBatteryStats if you whant to know what is draining it. But by personal experience, I think you should look at apps that use background data connection, like Facebook.