AC and H are two different study areas. Emphasis on STUDY areas.
While you may look at them as both broadly historical the way in which scholars write in each area is vastly different. Some will overlap, mich won't.
There are a lot more documents for example in early modern or Renaissance than there are in Ancient Egypt. This means we study these areas differently and a different style of scholarship is developed.
Do what you prefer... Ancient history or history of the last 11-800 years or so.
As for online, really it is individual, some people will do better attending, others won't. If doing it online you need to make sure you do it each week and not put it off because of other studies (which will eventually keep pushing regardless of time given).
I've HD'd units without attending any lectures, however I know generally people who attend lectures get better marks than those who don't (says lecturers.... a biased source which I'm sure can also account for more keen students).
It's pointless to consider a first year clash as a big thing given that you may encounter a clash in 2nd year or 3rd year or even 2nd semester 1st year anway.
Choose the areas within each study area that you like the most... e.g. American history, European History, Modern History (some of these overlap obviously), Asian history, Renaissance and Medieval histories, or ancient study areas, etc...