I did the part of the shorter route near Bishop's Stortford this evening to check on the paths and bivvy options.
The bridlepath that goes around Bailey Hills is somewhat agricultural. It was a bit bothersome with 55mm tyres, mainly due to tractor tyre tread marks, and no doubt the horses who have been ridden around there. But it's not too far, so you could suffer with more road-oriented tyres, and take care in the one or two places where paths cross.
Most of Baileys Hills is impenetrable. There is one place blocked by a locked gate in the corner of the field that looks promising. There's a triangular patch of long grass leading up to the gate that might be suitable, but there's much more space and enticement beyond the gate, leading up to a grassed clearing. The only thing I noticed as I rode further along is that there's a house which looks down across the field, which is on the far left of one of the photos. At nighttime they might see lights in what is otherwise a secluded spot.
The other option might be the edge of one of the grassed areas before Albury. Keep away from the farm, but there look like options around there. It is also close to The Catherine Wheel, which is a nice friendly establishment the western peleton have occasionally visited.
Do bear in mind that I have bivvyed exactly 3 nights, so my experience finding suitable locations is not unbounded.
Photos of the paths and the bivvy options are on Strava.