Dobster - welcome to this busy and informative discussion. Most of us on here came had a plan that was loosely based on some other plan and we have since adjusted it with input from Spoons and hearing about others training plans.
Like Carter I started with a plan loosely based on Hal Higdon but geared towards my busy work and family life. That said I have got up to 5 days a week from the 3 days a week I was doing in December.
Some questions for you and some thoughts on your questions.
You are obviously targeting a sub 3:45. But what marathon and how far are you into your training ?
5 sessions a week (running) seems about right but what mix of speed / interval / MLR's and LSR's are you doing ?
Your slow runs should be slow until you get within striking distance of your race and then you probably need to incorporate some MP miles into them. Slow on this thread is meant to be 10:00 min/mile. Not that we all do that !!!
The pace of your speed sessions will deepend on what they are and how long you run. So tempo runs should be 7:00 to 7:45 min / mile and intervals faster than that.
I do not do specific hill sessions but incorporate a steep hill into my MLR and LSR (same hill about 1 mile long).
I have always shied away from plans that are complicated. I like simple instructions. So I cannot help you on how to interpret your hill session. Spoons would be better at that than me.
The key is mixing the sessions up and not running as afst as you can every time.
Other activities are not necessarily a bad thing (I don't do anything else as I would not have a life if I tried) but doing too much can lead to fatigue and this will mean poor quality running and crap miles don't help with endurance which can lead to bonking in the marathon.
Do stick around as everyone on here must have learnt something as generally we have all improved from where we were when we started. 