You always want to get as big a mirror as you can handle...you have to take into consideration the size and weight for storage and portability. If you get too big a scope or one that's too cumbersome to transport you'll find yourself using it less and less. So, in other words, it's really a personal decision...(I'm not sure exactly how much more light you'd pick up, but if you're in for deep sky viewing and you have a good dark site, the 12" will show quite a bit more)...I haven't tried out a crayford focuser yet but as long as it's well made and at least aluminum (not that plastic Language Removed) and has a good amount of travel you should be good to go. Hope this helps.