Will I need to bring a folding umbrella?
It is a good idea to have a folding umbrella, but, you can always purchase one should the need arise.
What is meant by appropriate attire to enter museums and churches?
The term,  “appropriate attire” implies NO mini skirts, mini shorts, low-cut blouses or sweaters, thin strap sweaters or tees, flip flops.  
These rules are strictly enforced, and you will be denied entrance.