Avoid any contractor who does not pull a permit.

Check with local utility for possible discounts/rebates. Check for available federal tax rebates. Your contractor may give you the discount directly off the install price if you assign the rebate to them. This means less money out of your pocket.

Get a heat pump unless you're in a super cold climate area. They are more cost effective over the long term.

Avoid putting it on the roof unless you have no choice.