You will find the public transport information for Thessaloniki on
www.oasth.gr. From memory, it is bus 78 which runs between the airport and the KTEL via the city centre. You do not need to change buses. The bus station is just to the west of the city centre, there aren't any hotels close to it but there are regular buses so I would look for a central hotel. You could also take a taxi
https://www.hellenictaxi.com/ but I have never needed to and have always used the bus.