no you are not covered unless you are on his payroll legit.
#1 item you need is liability insurance $$$$. On a contract thing you might be covered under that companies insurance for that job only,' but should have a written contract, hand shakes don't count in court. Always best to have your own, then the Ins co can duel it out between themselves.
#2 registered with state as a biz. sales tax may be involved, varies all over.
#3 whatever the local area rules are sometimes you may need a city, town, village lic and maybe a county lic . could also be a per incident thing with locals. This a grey area rules requirements are all over the map.