I repeat, don't base your racket choice in what players use it, because the racket might not suit you. You shall try all the rackets you can and see which one suits you better, no matter what brand it is and then if it is too expensive so that you can't afford it you shall search for another similar option
How long racquets last depend on what care you give to them. If you take good care of them they can last forever... or a really really long time. The thing is that you will improve in a few years and maybe you'll have to change the racket since the one you have might not suit your new game. But if you take good care of it, it shall last as long as you want it to.
Regarding strings, you shall try the one that the racquet comes with and see if you need it tightened, or loosened, or whatever. When you will need it tightened is a matter of feeling it. When you feel you're losing control and you need it is too loosen you go and tighten the strings. But I don't think there's an specific timming for that. Also you can ask your soon-to-be-coach, if you get one, to help you with that stuff, they probably know a whole lotta more than what I could possibly know
I don't think there's another maintenance... not at least that I can think of.
Oh and I'm not good at grips and that stuff, you shall ask someone else about it