to vaccinate or not to vaccinate....that is the question

I have a mixed flock of hatchery birds as well as birds I have hatched (about 40 total) I have had up to 65 birds, but over the last few years, have lost some to either animals or mysterious deaths. I assumed this was just part of chicken farming. However, I am now reading up on Marek's and vaccinations (especially after talking with a poultry vet) and I am concerned about whether or not I should vaccinate (for the record, I don't think I have had any cases of Marek). I sort of was opposed to it at first (to try for more "organic" chicken farming) but I am reconsidering. I know that several of my chicks when purchased were vaccinated, some were not, and the ones I hatched definitely were not. So my question is for the eggs that I hatch, should I try to vaccinate them? Where can vaccinations be purchased if I should? Should I have any future chicks from hatcheries be vaccinated (my thought, yes)? How will this impact them all living together?

The way my system has worked, is I keep them in a separate pen until they are old enough to go in with the big birds (around 8-12 weeks) then I just introduce them during a free range time.

If this post needs to be under a different category, feel free to move it