How to store it?
In the fridge....
If you decide to store it in the fridge (if it is too hot outside) it has to be taken out prior to cutting it, 15-20 min will do just fine,
best for fridge storing option is to cut it all into the desired piece size and shape and then store it in the fridge.
Outside the fridge...
It's can be kept outside even in summer times as long as it somewhere in the shadow and a little bit of a cooler corner under a glass bowl and cut as much as you would like to consume.
Melting white chocolate ….
Not as easy as melting the dark chocolate since this contains no cocoa solids and it can easily turn lumpy, grainy and scorches rapidly.
It is all about the temperature that needs to be right and the whole idea is that the temperature isn't too hot.
If you melt it over a saucepan of warm water (better than microwave as you can be more in control over the temperature) you will need to choose a bowl that sits snugly over your chosen saucepan.
The bowl should not come in contact with the simmering water in the saucepan.
White chocolate scorches at just 44°C so the temperature needed is really a few degrees above our body temperature.
The best way to melt white chocolate is to chop your chocolate into evenly sized pieces or use chocolate chips, by stirring regularly.