Whatever fleet you build as UK, you are free to place in the seazones around UK. Then on the german players turn, he has 2 options: stay and fight against whatever fleet you might have built, or to run away.
This is correct. You may put new naval units in a zone that still contains enemy units.
What I used to do, as a high school girl, was to use a white chip under the control marker to signify it made it past the end of the chart once.
Now a days, I use a mapping utility even for face to face games. No limit on pieces, on chips or on money! (Also it’s set up instantly and you don’t have to put it away when you’re too drunk to see straight!)