Bandsaws tend to fall into two categories, for wood, or for metal. Basic difference is the speed of the blade however blade guides will be more substantial on the metal ones. I use a Startrite one that crosses both areas in that it has a 10:1 gearbox that can be introduced to reduce the speed to that needed for metal cutting. Of course the blades are different for wood than for metal but what ever material you are cutting, the blade pitch will need to be such that at least two, and preferably three, teeth are cutting at one time, so your 3 mm blank would need a fine toothed blade of 1 or 1.5 mm pitch. To cut a good straight line you need not only good guides, but also a deep blade. To cut tight curves you need a shallow blade. So your guides need to be either adjustable or interchangable so that the tooth profile runs outside the guide otherwise the 'set' of the tooth will be squashed by the guide. Guides can be either a slot cut in a very hard material, or an arrangement of ball races where the 'outer' guides the blade. For some reason that I don't understand, the 'slot' variety are considered more accurate (I would have thought it to be the other way round!)