You probably don't need E&O unless you design alarm systems. If you do, you'll need to know if you want an occurrence policy or a claims brought policy. Occurrence covers you for work you do during the insurance period no matter when the claim is filed (read years later), "claims brought" covers claims brought during the insurance period no matter when the original work began. Switching from one to the other can leave gaps in your insurance.
Liability is what protects you for work you do.
Bonding protects your customers if you steal from them. Most licensing requires bonding.
See an insurance broker. (Brokers deal with several insurance companies and can often get you a better deal than an agent who represents only one company.)
And then, get multiple quotes every couple of years. Insurance brokers (and agents) get a commission on sales and renewals that is a percentage of your premium. Typically 30% of the first year and 10% of each renewal year. Insurance rates tend to keep creeping up to increase their commissions. With multiple quotes, you can negotiate a better deal with the company you want.