i think there haven't been a lot of responses to this and to your post, Bravo, as it is a confusing subject. Some folks are adamant about doing things naturally and not vaccinating, others feel vaccinating is the way to go.
You first want to check with someone, perhaps your state vet (you can find them through your state dept of agriculture webpage). They will be able to tell you what is prevalent in your area. i would *think* you don't want to do unnecessary vaccinations.
i did some reading on Marek's when i had part of my flock put down for other reasons. The necropsy showed latent Marek's for several of the birds. My state vet said that all chickens have been exposed to it, it's that common. i read that vaccinating for Marek's does not prevent infection, and that there are some birds who will contract the virus from the vaccine.
The only thing i have vaccinated for here is Fowl Pox. This was because i brought a bird in last year, and during quarantine she showed signs of it. It's carried by mosquitos to other birds. The dry pox is not life threatening, but the wet pox can be. i just bought another batch of the vaccine and will be vaccinating the new kids in my flock soon.
Honestly, after dealing with our State Vet during my recent flock crisis, i highly recommend them as a resource. Granted, they are more geared towards large flock management and commercial operations. But they have the knowledge and expertise to guide you through caring for your own small flock. They can answer questions and provide insights you won't find by reading articles.