Wellllll, there are two types of people, people who hate 6PN, and those who love him. He's definitely a good position 1 ninja, if your pos1 is stacked af. But how good he is still depends on who you're going to use with him. He can still dies within the first 2 rounds of battles, but most of the time, he is immortal and hated for the typical 10 rounds fights. So yes, he's better than what you have currently, but not sure you'd wanna stay water main if you plan on using 6PN, it could work, yes, but he's better off with wind/earth main, or even fire main.

For what events to spend on, you'll have to figure out yourself from other forum threads. There's no one right answer for it, it depends on a variety of factors, including but not limited to, what are on sales, how much they cost, how badly you want them, how much longer can you wait, etc.

Power is always a good option to spend on, a good team is only as good as its power, after all. So that question is, again, for you and yourself alone. Only you can decide what you need most. Without us knowing your current power, and all the ninjas you own, there's not much we can advice you on the matter. And even if we know your BP, we'd still not know what you have upgraded and what you haven't, so you'd need to sum up which power function you have been focusing on and which you have been neglecting.