Reserve a stateroom NOW!
LOL yes, reserve a stateroom. Otherwise, it'll be a grueling, noisy trip with little or no privacy. I haven't done the inside passage for years. The last time I did was in a tent taped down onto the back deck of the boat. It was a fun adventure but I don't think they allow that anymore (and now that I'm 15 years older, it'd be less fun anyway). Staterooms make a nice oasis away from the on board summertime throngs.
As far as photo tips for SE AK, I live in Juneau and can help with some suggestions. What are you primarily interested in photographing/knowing?