I’d sort out the health issues first then worry about the riding/training.
SSBMV might be too much for you, switch to the LV plan and you can always add workouts. The HV plans are really for those who can dedicate the time and the proper amount of rest to them. I’m on the SSBLV plans but have moved all the workouts forward by one day so that the weekends are free for outdoor rides so I get the “best” of both worlds given the shorter, colder days at the moment in the northern hemisphere.
Indoor training is more precise than outdoor as you don’t have road junctions, traffic, gradients and the like to get in the way of whatever part of the workout you are doing - hitting a 20% slope just as you get to the end of an effort and should be in a recovery valley isn’t ideal.
HR zones are just as valid outdoors if that’s all you’ve got, particularly for steady state rides but be aware of things like HR drift.
I don’t think I could do a 3hr Z2 ride on a trainer, it’d bore me rigid! A short (1hr) SS or even Threshold session would be enough IMO and would give variety to your riding.