Being searched isn't a problem if you're not a terrorist, unless you have improper storage of things that have nothing to do with fireworks. Have any firearms that aren't stored properly? How about extra black powder laying around for them? As soon as you get a magazine for LE storage, you need to put your BP in ther as well. Although they won't give a crap about things like expired license plate tags on your car, they can prosecute you for any violations on things that fall into their jurisdiction, even if they have nothing to do with your magazine.
Also, you have to get state and local permits as well. Plus, you need to check everything out with your local fire marshall as well. Call your ATF office, talk to the local agent who's in charge, then talk to the local and state fire marshalls. It might cost you more than just the federal permits. Although I could get a federal permit while living here in CA, I couldn't get a local permit, so my money would be wasted.