Horsepower does not really matter on a regular size door. 1/2 horsepower is just fine. Make sure you get the proper angle iron if there is not already some there. I don't like the dinky ones that come with the opener. Make sure you have a T-25 stapler or else you can spend about an hour pounding those little staples that come with the opener into the wall. Just make sure you don't break the photo eye wires. Make sure you mount the photo eyes about 6 inches from the ground.
A tip about hanging the opener if you are by yourself, is once you have the front bracket mounted on the header, push the door open pretty high and put a vice grip below the bottom roller to hold it up. Then slide the opener over the top of the door. Reach up through the space at the front and put the pin in.
It's not rocket science to install an opener, but might take a little bit if you have never done it before.
A tip about hanging the opener if you are by yourself, is once you have the front bracket mounted on the header, push the door open pretty high and put a vice grip below the bottom roller to hold it up. Then slide the opener over the top of the door. Reach up through the space at the front and put the pin in.
It's not rocket science to install an opener, but might take a little bit if you have never done it before.