I am also left-handed and use the same rig, but it should not make any difference in how you set your rig up. The knife will work better on the left side, not just because that is the "standard" configuration, but because your belt buckle will keep it from sliding off when your belt is unbuckled. My wife likes her knife on the right, so I have to mount it behind a D-ring, or use a keeper. We replaced the modified steak knife (which is very sharp, by the way), with a titanium knife with longer blade, longer handle, straight edge, serrated edge, saw edge, point, and line cutter.
Your belt buckle should not have to be changed either because it will be set up as a right-hand release, which is industry "standard," and consistent with most other setups. Consistency is important if someone is trying to help you if you ever need it.
My SMB is inside of a Dive Rite clipper pocket, mounted as far back as possible on my belt, near the BP. My wife's SMB is clipped to one of the holes on the bottom of the plate. You can also run a couple of pieces of bungie through the bottom holes and secure your SMB that way. Just make sure the bungie is tight enough so the SMB won't slip out.
I also used a small bungie loop through my left chest D-ring keeper to secure my inflator hose.
As you know, left-handers adapt to the right-handed world every day, without even thinking about it because we have to, but setting up your rig is no problem at all. My rig is set up just like the instructions indicate, but bottom line, you can set up yours any way you want. That is one of the great things about the BP/W system.
Hint...make sure you slide that little round piece of rubber all the way up your left chest harness before you slide your D-ring on and thread the bottom of the BP. If you forget, you'll have to start all over! Just follow the instructions.
