You'll get opinions for all of the above that you mentioned. While trending now seems to be more towards adding all flavoring components into secondary, or at least waiting until fermentation is done then adding them late into the primary. the execptions being cysers, pyments, braggots and acergylns ofcourse.
Personally I now start everything as a traditional mead, I try to be diligent in yeast managment (temp control, aeration, nutrients) and make a simple mead that is all about the honey used first, something I could sit down and enjoy a glass of if nothing more was done to it, then I add my fruits, spices, oak, etc. etc. depending on the end product I want.
I have also been racking into a secondary a gallon smaller than primary, so a 5 gallon primary goes into a 4 gallon secondary onto whatever additions I want and the remainder goes untouched into a 1 gallon carboy. This leaves me some of the original base mead for topping off anytime needed or if I go a little strong on a flavoring I can "thin" it out some without diluting with water or plain honey water. Worst case scenario, I have a gallon a good traditional mead win/win.
With all fruits a little pectic enzyme dusting prior to adding to your mead is helpful for extraction of flavor and color but nothing further is really needed, with cherries or any pitted fruit It's best to remove the pits as they can make some bitter flavors that are unappealing. And instead of crushing or pureeing which can hinder the removal and clearing process later, pit your cherries, dust with pectic enzyme if you have it then freeze/thaw them, once is good, many prefer to freeze them twice, this causes the membrains to be broken down by the crystalization of juices during the freezing, it ensures getting the most ouf of your fruit and also removes any chance of any wild yeast or other bad stuff of sneaking in.