It’s okay to do yourself, the requirements can be found on the internet. But if you just want a smooth process by hiring someone, at least find a few other agencies for quotation.
If spouse it’s actually easy that you can do it yourself. If it’s for fiancé I’d suggest you find an agent based on US first to consult (there are many in big cities like LA/NY/SF)
Anyway good luck, it’s US visa won’t be too difficult if you are legit and clean citizen