There's a couple videos on youtube for pickling herring and quite a few on the internet. Poland, Dutch, German etc recipes. They all do it pretty similarly with some variations between creamed mustard or mustard seed used and some of them add the simmered pickling mixture to the jars fairly hot, partially cooking the fish before pickling. While other recipes say to let it cool first then add it. I'm gonna make pickled rollmops myself since I already have a bunch of homemade pickles, veggies etc. I gew up eating them a lot as my dad bought them pretty regularly but he never made them from scratch.
I smoke a lot of fish, meats and cheeses but not too sure how smoked Herring would turn out. Think I'm just gonna stick to pickling them.
As for bait there's lot's of recipes for that online. I will use the smaller ones to use whole in teaser heads, the medium/large sized ones for cut plugs, and for the largest ones I use them for strips, getting two from each large herring. I'm curing them all up ahead of time then vac pack and freeze them. Cured then frozen/vac packed will keep them in much better shape than freezing them uncured. Getting the excess moisture out of them pre freezing helps the longevity of them a lot and makes for much better, more durable bait when thawing them out to use for bait.