The mistake I've made in the past is ending up with a mixture of the wrong stuff, by that I mean we could argue all day over passive or active speakers and there's no right or wrong in reality but I ended up with a perfectly good passive desk and passive speakers which is of no use to anyone without an amp.
Make a decision early on which way you want to go and stick to it, you might get a mixer from one place, speakers and stands from another, but you don't want to end up with a nice passive mixer only to find a great deal on a powered euro desk the next day or a pair of powered RCF speakers after you've bought the powered desk!