My $0.02 - it's cheaper to buy one set of good gear that does the job right, than to buy something the does half the job only to be dissatisfied and upgrade two weeks from now.
For SQ, do NOT skimp on your H/U. Save a few extra bucks, be patient, and get a good H/U that will do what you need. You will not regret it.
As for mixing tweeters, it's generally not a good idea to mix different speakers and this is why: they all have different characteristics and qualities, and when you're tuning it makes things much more complicated.
Two things to consider are dispersion and frequency response. Example: one set of speakers might be smooth and have great on-axis response while the other might have better off-axis response and be too bright if they're aimed at the listener.... I'd say stick with all the same type of tweeter.