I would highly recommend before making any cuts to have a read through the links I posted previously, we have just seen a person trim too much off their abdomen and kidney and are now either having to add extra material of find replacement pieces.
For those of a skinnier nature like me I built to the average size and added foam behind my abdomen, which will hold it outwards and take up some slack when tightening your belt and things won't get as squashed.
A few issues you may want to address first is the overlap of the backplate and kidney which will be pushing your posterior down and outwards, also the thighs hitting the posterior, there may need to be some trimming of those so you can actually walk.
Strapping makes a BIG difference to how everything will sit.