Rattler lots of good advice. Some things to add.
Sub 4 is not a given off a 1:50 half. It's very tight in reality, running flat out. A few friends have done 1:46 halves, and still not gone sub 4. Over confidence is dangerous, respect the distance.
Other point, worst thing to do is forcing your training pace, especially on the long run.
Forcing yourself to run at pace X - race pace or near as will tire you out every week, increase risk of injury. Long run, slow, should always be able to chat for some of it, nearer the time, some miles @ MP or a fast finish.
4 runs a week is fine, 3 some weeks. cross training is important too,
You can manually add runs into Garmin connect even without the Pod.
Coach said good advice to me at one point about plans -
it's a flexible program not a prescription
Enjoy the first one..