Welcome to the forum.
A used pump can only be evaluated properly by seeing it and listening to it. An 8 year old pump that has been protected from the elements should be in pretty good shape. Mine is in a poolhouse and has been going 13 years with no problems. Some that have sucked a lot of water mist in and/or have been a home for insects can be pretty much shot after a few years. Probably rusted to the point of not being able to take them apart. Bugs and webs can block air passages leading to localized overheating of the windings. So, if you can, at least look at it. Better still, listen to it at least for a few seconds if it doesn't have water in it. Also look at its size. Typical AG pool packages come with a way oversized pump so you may decide to change it anyhow.
As for heaters. Heat pumps lose efficiency in cooler weather, just when you need it. I don't know what they run BTU wise but gas can be as high as you want it, certainly much more than any heat pump. My educated gut would say go with gas in your climate. Maybe someone else has other suggestions and ideas.
Hope this helps.
Al