Strength is defined as the ability to exert maximum force against a resistance, once.
If you are not increasing the resistance, you are not increasing strength. Increasing reps or time trains endurance, not strength.
i do not follow Mo Farah's running programme, because I am not Mo Farah. I would not follow Mo Farah's strength programme because it is collection of rehab exercises that would be suited to someone who has been bedridden after a severe accident. Presumably he has ben paid to lend his name to that monumental pile of tomfoolery.
How often you should train would depend on your age and some other factors.
Yep. One mile with a break in the middle and I felt terrible. shin splints, aches, calf strains.
I started reading up and followed the advice in Chi running by Danny Dryer.
I'll summarise. Shorten stride and aim for a cadence of 90 or thereabouts. Go slow, keep going slow. Do not try to go fast.
Go so slow that you can keep your mouth closed and breathe through your nose (not so easy in winter, I'll grant you). This seemed just about impossible at first, but it can be done if you relax and run with a short stride. If you are breathing hard, you are working too hard.
Get a plan. I built up the distance on one of my three weekly runs by five minutes a fortnight. I measured running time rather than distance because it's a lot easier to do with a cheap imitation Timex watch. I kept the other two runs short.
As the distance built, I found that I was able to do the shorter runs more quickly, but I didn't really push for that, it just happened.