I, or I should say my wife does my visa, so I don't have enough experience with agents to recommend someone.
Because getting around Bali can sometimes be a bit of a nightmare, I would suggest looking for one that has an office in the area you plan on living in.
My other suggestions would be to choose a company that has been in business for a long period of time and has a physical office, not someone who runs their business off the back of a bike.
Insurance has been discussed here numerous times. Unfortunately there is never any great conclusion. Maybe get travel insurance for the first few months then decide on something more permanent.