This board is full of archived reports, many quite recent, on the Bay Islands Beach Resort (aka: BIBR).
October can be kind of rainy and rough from the North. Water temps on the surface are consistently 80-84 degrees year round. Here is a weather log (albeit from the South Side) for that month in 2006:
http://www.docksidedivecenter.com/WeeklyLog102706.html You can page back through the weeks as far as you wish, but you'll see that October 2006 was quite sunny!
Favorite dive spots are largely irrelevant information as the DM will take you to where he judges your abilities and weather will mesh well. Roatan is not about mileage and making tracks. It is about hovering and observing closely. It's all in the details. Sure- you can go there and look for all of the same stuff you see at any Caribbean Island. Focus your eyes on the smaller, camouflaged stuff. How?
Just follow the DM and be prepared with good buoyancy to get in close to the cool microscopic stuff he will point out. Do as much night diving as is offered. That's when Roatan really sparkles.
Things to avoid? I think anyone with Roatan experience would recommend
avoiding the feeding of the sand flies.
Most would recommend Salva Vida Beer, Flor de Cana Rum, talking with the locals, having dinner on the West End, DEET, and in general, logging a lot of bottom time.
Go, have fun.