is there a certain type or size of laptop fan I need to use or can I use non HP fans?
the outer shell is the heat sink and bracket. if you can pull the fan out and read it part number you may be able to cross ref it.
there are three main power issues with the old/new fan. the on amps it pulls when it starts up. if the new fan uses more it could burn out the mb. then the max amps and voltage. as long as the new fan is rated the same you wont have an issue.
most fans are stock sizes in mm. 20/30/40/50mm. you just have to measure the old fan. comp like digikey should have a replacment.