You can keep the same bearings when you change wheels. Properly cared for bearings should last a year or two. I go through a set of wheels about every other month and I get two sets a year from my sponsor. Even with the discount on additional sets, that would set me back quite a bit. If you ride on different wheels for different surfaces, you might want to get a set of bearings for each different set of wheels you use. It will save you time in switching out the bearings whenever you use a different set of wheels.
I'd stay away from the Lucky bearings. The ABEC 5 and 7 bearings are not serviceable, so there is no yat to clean and lube the bearings. The Lucky Swiss might be good, but I don;t know anyone who has tried them. If you want a good value bearing, go with Bones Reds. If you want the best, use Pig Swiss