Hmm. Well, if you just want to help bees (and other insects?) then one thing that can be done is to plant natives to supply nectar and pollen for the wild pollinators. As a plus, perhaps such plants could end up with similar early bloom times to your plum tree and attract said insects to your area to assist with pollination? Just a guess. A good resource on that (for just North America, I think) would be Attracting Native Pollinators by Storey books.
Other than that, I would say to get in touch with the local resources that you mention. I used to be a part of the Toronto Beekeepers Co-operative, and there was plenty of people there willing to help, and who had knowledge catered to the specific area. Beekeeping can be a whole other thing in comparison to backyard chickens, so I tend to think it’s best to get some initial exposure and experience before committing to your own hive(s).
As a side note, and not that the honey was my reason for joining up with the Co-op, but I still find it hard to believe that the honey we got from our first round of extraction was the best honey I’ve ever tasted. I was told that it was probably because of the wide range of plants that people kept in the city and which the bees fed on, as well as because of a wild area nearby which provided for a diverse collection of natives.
I hope that helps.