if people on those farms do not come on ur farm u shouldn't be worried about it. with a backyard flock that small i do not reccomend any vaccines. u should be fine unless ur flock is exposed directly to something so no worries.
The two common vaccines are mericks and cocci. Cocci is everywhere and so really, just expose them young and use medicated starter to inhibit it's growth so they can build immunity. Mericks is probably not an issue with commercial houses since they should all be kept tight and disease free for economic reasons. Just follow standard biosecurity and you'll probably be just fine.
I vaccinate for Marek's disease, but that is all. You can buy the fort dodge vaccine and administer it yourself. It only comes in a 1000 dose vial! BUT it is relatively inexpensive (~10$ at our local feed store). You can also order it from online farm supply places, but then shipping cost is more than the vaccine as it has to be shipped in a cooler.
To be really sure too, you can check with your state agricultural extensions office to ask what are the problems known in your area. If you do go for mericks vaccine, hatcheries will do it for you for something like 15 cents a chick.