Anyone can learn a spec or class, they will not perform with 100% effectiveness, but 80% is not out of the question. There are people here who can help, look for WA rotation helpers, read up on your class switch specs.
Arma is a good example of this, he knew 2H frost was garbage time so he dedicated himself to learning Unholy. Everyone is capable of the same thing. You dont need to spend all week on it, but an extra hour or two per week should be acceptable. Learning during raid is not that effective (see me on IM last week). Any skill you currently have can always be improved upon, just ask for help, someone else in the guild will be more than happy to assist you if you need it.
As for bosses I think clearing all bosses we have downed, including IM, then doing a few Mythic bosses would be good.
Truth