Thank you all, this has been very helpful. What I'm coming around to thinking is that a quality epoxy primer is the "gold standard" for priming and will probably ensure the plane outlasts me, but there are various other degrees of protection down to no priming on alclad that also provide some benefit. The challenge seems to be much like choosing which airplane to purchase: finding the one that best suits my unique combination of environment, build ambition, and expectations. It sounds like at the very least the aircraft won't fall apart on me a year after I finish it no matter what unless I really do something terrible.
Now having said that, I think I'll probably start out at least with applying an SEM primer as I'm very pleased with how tough it seems to be and how it looks while being simple to apply with manageable (in my build environment) hazards. Steel parts will get that plus a finish coat.
I've still got a couple of months before the first kit arrives to change my mind, but at least I feel better about having a path forward.