Some agencies teach to use the drysuit as your BC, others teach to use the BC as a BC. Personally I use the BC as a BC and try to run the minimum amount of air in the drysuit that I can tolerate. Only add air to the drysuit to alleviate squeeze, or if I get cold. As you are early into learning the dry suit try to keep your feet lower than your head, don't run much air in the suit, and also try to stay near something you can hold onto just in case like a rope or a line until you get the hang of things. I started out in dry suit diving using military thermals and other half steps to proper drysuit thermals. While it is doable, there is a much larger learning curve finding non dive thermals that will work and keep you warm in your conditions. If I could do it over again I would have skipped the non scuba thermals and just went to the correct ones right away. Would have saved a lot of aggravation and shivering.
It isn't that hard, but it is different and there is a learning curve associated with it. Hopefully buy from a shop that can teach you, but more importantly that you can dive the suit with on a regular basis as you will got a lot of education and experience just diving it, with a good mentor.
I am a fan of DUI dry suits, but there are lots of good companies out there.
Brent