borders and hassle free checkout

gaphotoedge

In order to make checkout easy, I have only made available certaiin image ratios. 2:3, 1:2, :1:1, for 1:3 panos, the customer has to contact me directly. what if a custormer wants a stretched canvas? my images don't lend well to wraparound. I have the 'chart' stating final page size for a certain size canvas print. ie: abt 01.75 inches extra on each side. so I can adjust the image within that before uploading, probably making it black, which seems to suit my images. can i then use these same measurements to border prints in general? then the 'bleed' when framed would work...yes? a black (or dark in a suitable color) than stuck out from under a frame would be another border. and easy checkout for the customer....what problems am I overlooking?
thanks,
gaphotoedge