It's entirely up to you. The advantage of racking to a second fv and cooling helps the yeast to drop out thus resulting in less sediment in the bottles and a clearer beer. Some do it, some don't.
If you batch prime you mix the sugar with a little hot water to dissolve the sugar then add to your beer, generally in another bucket / fv just before bottling (some mix it with a little wort and heat on the hob until the sugar is dissolved).
In all of the transfers between fv's & bottles, be very careful not to splash & introduce oxygen.