Is there a way to change the amount of items that stack when you store or trade them?
yes, press shift+click item you want to split..

Lv160 is the current cap right? If so how long has it been the cap and will the cap ever rise?
how long: I forgot
will it rise: of course, usually every expansion will increase the cap by 20..

Ok thanks. The reason I asked about the cap was to see if it would ever happen and get an estimate of when lol