We migrated from the classic calendar to the new calendar earlier this year. We too had individual calendars for each building. For the sake of migration, we created new stake calendars for each of those building calendars and imported each classic into the new calendar. We also created one additional new calendar called "Stake Resource Calendar" which would hold all non-ward based events i.e. receptions, family dinners, etc... After the import of each classic building calendar to the new building calendar, we had to go through each of the building calendars and add the location/room assignments and them move them to the "stake resource calendar". We were fortunate that our old process provided all the detailed reservation information (ward, event, contact info, building, room) in the description. Moving them to the resource calendar helped to keep track of where we were at in the migration as events were moved from building calendar to resource calendar. When the building calendar was empty, we deleted it and the migration was done.
Prior to the v2 release, building schedulers were able to create or move events to any ward calendar. It was very handy to have that ability and we were able to take a lot of events off the stake resource calendar and place them where they belong on the ward calendar. With v2, that ability has been removed. It was definitively a great feature that hopefully will be restored at some point in the future. My guess is that it won't, but one can hope!
Once migrated, we (stake building schedulers and clerks) made a concerted effort to train ward leaders so they fully understood what changes were coming. We met with bishoprics, clerks/exec sec and event trained ward councils on how they could schedule building resources using the new calendar. Some embraced it fully. Some didn't and still struggle to grasp the distributed concept, event when the church itself has produced videos and documentation that outline the benefits of the new system.
The new calendar isn't perfect. I will say that as a stake building scheduler, my call/email volume has been reduced significantly. I find myself being more of a coordinator rather than a scheduler. The scheduling responsibility has been pushed down to the wards, where it should be.
Hope this has helped. Good luck in your migration. It may be painful at first, but the sooner you make the change, the better off you will be in the long run.