At the moment, Dorico does not include any special casting-off behaviour for the ends of right-hand pages, e.g. to try to ensure that there is a rest suitable for a page turn at that point. We will probably add such things as options in future versions, but I don’t expect this to be in place before version 1.0.
You will, of course, be able to choose to end a system or a page anywhere you like – in the middle of a bar, if necessary, including in the middle of a beamed group, or even in the middle of a (nested) tuplet, if you really have to (though please do try to find another solution that won’t give your players the heebie-jeebies).
Dorico is capable of producing much tighter spacing without collisions than any of the other GUI-based scoring programs, because of the fundamentally smarter approach it takes to spacing. You can read about this in several of my development diary entries, including this one:
Of course there are plenty of parameters you can tweak to control default rhythmic (horizontal) spacing, and ideal vertical spacing, and you will be able to adjust both of these also on a case-by-case basis in Engrave mode as needed.