http://jianshe.com.au/js80py
As two strokes are slowly being legislated out of our lives spark plugs are starting to be hard to get. As was suggested: try a "6" (BPR6HS), but watch it carefully, as it seems that one heat range is a bigger jump than "normal", or what one would expect. (running the engine too hot can get costly)
Where I live 6's and 7's are easy, while 8's are a problem, and have to be ordered by the box.
Yes, depending on the size of the oil tank, multiple fill ups to one oil fill is normal. You may want to switch to a synthetic 2 cycle oil if plug oil fouling is a problem.