well that Martin, is how superb wide-field imaging is done! next time it'll be us asking you for advice! your next challenge is a mosaic
i don't mind the diffraction spikes either, but i'd try looking on ebay for your aperture masks.. i've got lots of step-up/down rings etc and other things like that for peanuts in the past.
if you do that though, you'll probably find the bright stars get lost and so you will start looking for a blur filter to make them big again (in separate exposures to be added later) and then you'll be unhappy with how un-natural they look and start a lifelong search for the perfect blur filter and you will never be satisfied.. how do i know this you ask?..
Phil