Re: What's the appropriate primer/sealer for new plaster walls?
If you use Lime Paint (from Virginia Lime works, others) you needn't wait at all to paint new plaster; nor is it necessary to use a separate primer. And it is a completely green product, possibly zero-voc, but I didn't check that. I have used it and there is a lot to recommend it. It gives a more home-spun organic look. It is very flat in finish. By dappling a second color, some very nice effects are possible, almost like a faux finish.
Remove not the ancient landmark, which your fathers have set.