1) No, polish/sealant brands do not need to match. After polishing you should wipe down the vehicle with a 50/50 mix of Isopropyl alcohol to distilled water mixed in a spray bottle to remove any traces of polish. This process is just like using an instant detailer.
2) No, wax is not necessary. A good sealant will both look good and protect against the elements. But don't think wax is just for looks, Wax gives you "sacrificial" protection. As in your coat of wax wears away first, it's worth it. If your budget is tight try Griot's Garage Carnauba Wax Stick, S100 Carnauba Paste Wax or any Poorboy's World Natty's Paste Wax.
3) I've only used the Klasse twins and WG DGPS 3.0... I want to recommend either of them.
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As of Oct, 20 2009 I have quit smoking cigarettes, cold turkey. After more than a decade of smoking at least a pack a day...
5 months down!