Crossover Soldering

Hi, I am new to this forum, and this is my first post... So, hello to all.

Question : I'm making my first crossovers, and will be soldering with silver 96/4 solder. Should I use a flux/resin while soldering? If so, any recommendations as to brand/type?

Also, if I do use a flux, even if it's a no-clean flux, what should I use to clean up the soldered joints?