WELCOME ABOARD!
1) Yes
2) No
3) Read the manual. It explains everything, including doing a short patrol (the game only lets you start on the first day of the month, so the time has to be dealt with), so after the time spent in port you will sail again just before September 1 and be in position when the war starts.
Or you can be like some of us and make a goodwill tour to spy out all the British ports. Lots of pretty stuff to see for those who care to look.
You wouldn't know war was going to break out, but on August 19 BdU sent 14 u-boats to the north Atlantic, 'just because'.