Elliot... the more running you can manage the quicker you'll improve, the only time LESS running is beneficial is when you're risking suffering overuse injuries.
In relation to the last point, yes - the more time you spend on your feet in one go, the more your body will get used to it and therefore improve your endurance - pushing your body to carry on even when it's tired.
In terms of what would be most effective - there are a huge amount of training schedules around so I'm sure you could find one to suit, they all tend to stick to the Hard/Easy rule, and will incorporate at least one rest day. Personally I'd run:
1 - Easy
2 - Hard
3 - Easy
4 - Hard
5 - Easy
6 - Hard
7 - Rest
But what those runs consist of are entirely up to you! Check out the
RW website for more schedules than you can shake a stick at, and they have some 'smartcoach' system as well that comes up with a plan tailored toy our current ability.
Sorry it's not a definitive answer to your question - but hopefully it'll help a little!