Hey i started with a normal also and shes my favorite one, so nice and a great pattern. Now by the time you are in the market for a Spider, you could get one for $125-150. I got mine for $200...
Oh yeah also to answer your question about what sizes to put in what tubs. It all depends on what size tubs you have ready access to. Me personally i can get 6 qt, 16 qt, 28 qt, and 41 qt tubs. You can keep a baby in a 6 qt until they are around 200 grams, some people say 400 grams, but that's a little cramped. I personally use 16 qt tubs for all babies up until about 500 grams, then i move them into the 28 qt tubs. Only really large ones will get a 41 qt, but i don't have any that large yet, so no need right now.