I've got the same problem. All I plan on doing (haha eventually) is to fill the gaps around the oven with chipboard or similar, then clue on some aluminium sheeting to cover it all up. Aluminium is cheaper and eaier to work than SS, and I have an aluminium finished oven that it matches well.
As it isn't structural, you should be OK to do whatever looks the best.
Some days we are the flies; some days we are the windscreen