November 9th, 2014, 17:28
You don't even need png as a format....PSP's default format will preserve trans.
Alignment can be an issue without markers...hence the bmp option provided the layer opacity is at 100 and you have an easy fill colour to cut out again once applied to a layer set.
Life's just all too easy with these layer thingies....I spent the first decade or two of CG doing it all flat...you know, like good old 'painting'...;)
If you do go down the road of making your own....make it as big as your system can handle....4096 is the go...
You'll hit 32bit proggy memory issues sooner or later...but I've found PSE 2.0 survives better than PSP6...so when PSP chokes I switch to PS Elements ...;)