If this is a real place, the scale can be found from a conventional map of the area. If not, then your guess is as good as mine.

That's why I generally draw my own arrowheads and copy and paste them on the ends of all the arrow sticks.

Are you saying it was too slow on the larger map? That can make things seem uncertain. Other than that things should behave the same way if you do them the same way between maps.

If things are slow now before you ever add anything but the land, then it could be that you have too many nodes for comfort. The problem only multiplies as you add terrain and trace along the existing coastline for the edge. If this is ringing true to what you are seeing, I recommend using the SIMPLIFY keyboard command to reduce the total number of nodes. You would be surprised just how many of the nodes in a coastline don't actually do anything because they are too close together to be noticeable.

If the lines are already drawn you can use Change Properties to give the lines a line width if they have none, or to make the line width thicker. Rather than guessing how thick the line is to start with, you can use List from the Info menu to find out how thick the line is before you start.

There's a loop in the line at that point. If you look at it as if it was a road you were driving down starting from the left, when you get to that point you are heading to the northernmost point first, and then the southern point second. Jim is right - you just need to decide which of those points is the one you want and delete the other one using the delete node tool |CC2DELNODE|.

If you are having trouble hitting the point it's not at the very tip of the line because the line has a width. The nodes are in the centre of the line width, so it will be a short distance in from the tip of the point.