1. If protected from extreme things like wind/rain/predators, your brooder & heat plate should be OK in a garage or barn or shed. It's best to listen to their sounds & watch behavior when figuring out if temp is in the correct range.
2. Vaccinations are usually for Marecks- given at hatcheries if requested. It's not cost effective to vaccinate handful of chicks, so most broody-raised chicks go un-vaccinated. Marecks is a neurological disease that can affect birds via dander exposure to other chickens carrying it. I believe they can catch it at any age.
Medicated feed is a preventative for cocci. Cocci can quickly spread to all the chicks making them sick, weak, lethargic, loose poops/ blood in poop. All the chicks can easily be treated with Corid if they contract it, but it could also kill chick if not caught in time and treated. It mostly affects chicks since they don't have as much immunity, so that's why some people choose to use medicated chick feed. There are pros & cons to everything & plenty of opinions.
There's no one, single "right" way to raise chickens, so like many things in life, you gather info and make a plan that best fits your needs.
Thanks for your thoughts! Do I need to do anything to the food on day one to make it palatable for them? Like water it down or try to feed it to them?