Ben, in page 3 i posted a link to a very good website that explains everything about zones, organizing your training etc, it helped me a lot to plan my runs.
Your routine so far looks good on paper, maybe without knowing it, you are following the zone training principles, the only thing that would worry me is that doing it non planned, and just based on your feelings, could end overtraining you, but it all depends on how well do you know your body and understand those feelings.
As for your questions related to your training:
IF I FEEL SOMEWHAT TIRED: 35-60 minutes, avg heart rate 140-150 = Recovery run
IF I FEEL VERY RESTED: 35-50 minutes, avg heart rate 155-160 = tempo runs
Good Heart rate calculator that explains what you train in each "zone"
Heart rate zones | Running for Fitness
Graphic of zones:
The only thing i miss in your training, once you want to go further, is interval training and/or fartlek, to improve your speed and resistance to anaerobic efforts. Both consist mainly on doing some minutes/distance of big effort followed by some minutes/distance of slow run to recover, then fast run again etc for a few times , it's a way of training in different zones in a single session (that was a very basic explanation).
Anyway i'm not an expert, in fact for what i see in your strava times and distances, you are in better shape than me, but i have read a lot the theory behind running, in fact it's what i do mainly now in my rest days (today) as i'm a bit obsessed with running now
