I have not used Swissvax so I cannot give an educated opinion on it. However, it is supposed
to be a very good wax. I tend to use Chemical Guy's 50/50 wax on my Alpine White BMW.
As for your second question, sealants are to be applied after polish/glaze (optional depending on your paint condition) and before wax. Sealants will not bond to carnauba wax, you should use a soap such as CG Citrus wash and Gloss properally diluted to remove any previous wax, then you can clay your car, that way your sealant can bond to a nice clean surface.