Have you measured your maximum HR by doing a stress test to see how high it can go? Or did you just estimate it using 220-age? If the latter, it's possible that you don't need to be running that slow after all. For example, my max is around 215 (I'm not 5 years old) and 60% of that is 129 (which I could run at on a super-easy run in nice weather). 60% of the formula for me would be 110, which would not remotely correspond to any running I might do.

Having said that, I don't train by HR so can't answer the specific questions if you do know your max, except to say that (1) probably not - doing very slow HR-based recovery runs as part of any other schedule can't be a bad thing, BUT the real reason to be using HR is supposed to be to moderate your effort based on your ability and current fitness. So make sure you have a sensible and realistic frame of reference for deciding your pace goals. (2 & 3) can you not order your types of run/rest days based on the plan you have been following, if all you want to change is the HR bit? Presumably it still has different kinds/intensities of run in it?

I've done nearly all of my training in conjunction with HR data. That started in the spring of 2013, so I have a pretty good idea of what works (for me).

First, the 220-age formula for maximum HR only works for a small percentage of the population. Or put differently, it is so conservative that virtually no one is at risk of running their HR too high. That is the first problem to be solved. There are ways of testing that, An actual stress test can help set max HR and zones, If there are no underlying health issues there are other ways of self-testing.

I use/used a 30-minute running test to set all of this. It is a maximum sustainable run for 30-minutes. I do mine on a track so that I can see whether I am maintaining/sustaining a maximum pace. My max HR has tested as high as 199-203 at the end of one of those runs. Now, to be honest, that is uncomfortably high for me. So, I set my HR max at 195. The program I use to calculate the zones takes the data and approximates the lactate threshold value as the top of zone 4 (basically the average HR for the last 10 minutes). If you actually look at the data you can see the actual inflection of the HR as you run one of these tests.

That being said, my runs break down this way.

Recovery runs and "easy runs" are done with almost all of the run in zone 1 or at a very low level zone 2. This is a slow run (though it has gotten faster with conditioning), but just fast enough so that running form does not go way out of whack.

Medium-long and long runs (10-16 miles and 16-20 miles, respectively) are run almost exclusively in Zone 2 unless the run has other requirements like intervals (but they are typically classified differently) or a fast finish run (which will typically be run in Zone 2 until the fast finish kicks in and then that is typically a Zone 4 run).

Tempo runs are typically slow (Zone 1 -2) at the beginning and end, then faster (Zone 4) in the middle pressing towards the lactic acid threshold and sustaining that over the requisite distance or period. An example might be a 14-mile run with 12-miles at half-marathon or full marathon pace (my plan uses both paces for training in different phases).

Finally, my hardest runs are the VO2 max repeats. These really are the hardest workouts I do once per week. The idea is to press the run to the maximum during the time/distance and then walk/jog to allow a full recovery before the next cycle begins. The toughest ones aren't the 800m repeats, its the 1000-1200m ones of pressing to at least my 5K pace. My heart rate using climbs into the low end of Zone 5 during those sprints.

One other thing...the HR zones have moved only slightly over the past three years but the speed in each zone has dramatically increased.

The thirty minute CP-30 test is a standard test protocol (CP=critical power). Fitzgerald or Pftizinger also describe this approach. Another protocol is a series of 800m repeats to set various zones and thresholds. Mine (CP-30) happens to be incorporated into the iCardio (Digifit) app, though it does overestimate my VO2max based upon my maximum heart rate and resting heart rate. The velocity based VO2max is probably more accurate (Daniels). But the heart rate zones match other approaches I've seen.