I thought the same thing about let/letting!
Not everyone has to put down 6 months rent. But I would say about 50% do. Just depends.
No, there is no time limit that you have to be in the country before you can open an account. What you do need, is proof of address to open a bank account. I'm sure you can see where this is going. If you don't have a bank account, you can't get a lease... Without an address you can't get a bank account... it makes those first few weeks here fun! (oozing with sarcasm).
Yeah, if they'll let you open an account with someone, that could be a great solution. You *may* still have the proof of address issue though.
You'll figure it all out in time. This is one of those things you really can't do until you are here!