The two programs aren't designed to work together.........yet. That's going to take some time for Adobe to really integrate them. The new Lightroom CC is for a different crowd right now. It seems to be for people who want to quickly download images and do a little editing and then share those images on social media. All of the tools are not in Lightroom CC. I find that the synchronization between the two programs isn't as complete and as smooth as I would want it to be. My suggestion would be for you to just experiment with it for a while and watch it grow and develop. Don't try to make it a serious part of your workflow right now.
There are three major problems with trying to migrate a large catalogs. First is that you need enormous amounts of hard disk space to do it before everything is uploaded to the cloud even assuming you have the cloud space to do this! This is prohibitive for most people with large catalogs and is very hard to work around. Second is that Lightroom CC's features are extremely limited. Do not expect to be able to do even 10% of what you do in Classic. As Jim says it seems to be targeted towards the iPhone shooter crowd with very limited needs. Third is that communication between Classic and CC is limited. Classic is smart enough to see that the images in the cloud are the same that it already has and will link the new cloud images to the ones it has but a lot of properties (keywords, etc.) do not sync. Also new imports into Classic do not end up in CC automatically. So you could become out of sync very quickly and have different things on both sides.
I am sure LR CC will get better and have more features. However Adobe has indicated the sync features in Classic will not be improved. This really means that if you now need anything that you can do in Classic say like actually printing, hierarchical keywords, publish services, etc. etc. you should stick with Classic and just play a bit with CC. The interesting thing is that you can simply sync collections from Classic and they will show up (albeit just smart previews) in CC and you can play with it that way.