Keeping the top cap just snug, and not too tight, is key here. Too tight and it's murder to open/close liquid control. The o-ring spreads wider as you tighten the cap. The wider the o-ring, the harder it is to turn the liquid control. If you find the control is hard to turn, loosen the cap a little till it isn't.
As for the base/cup coming apart, what Imeo said is best. Get base and pin where you want it, and tighten the upper control nut down good. After it's snug you further tighten the whole thing holding onto the cup and base. It won't turn much, if at all, but it will help hold it all in place better. Holding the ceramic housing with a rag, or paper towel as Bishop says, will keep your fingers from getting ripped up.
If the top cap is on correctly (not too tight), and the liquid control is fairly easy to turn, you'll not ever unscrew your ceramic housing during use.