Mostly I agree with everyone else. Test if first, synthetic quilt on top, and make sure it doesn't compress the down bag. One big thing that is important is that your pad arrangement is backwards you need a full length ccf and your second pad can be whatever you would like it to be.
The VBL thing is very tricky, there are two ways to do VBL, clothing or bag liner. I didn't like the bag liner when I used it last winter, I am going to try clothing this winter. VBL is only necessary if your trip is longer than 3 nights. You would be surprised how quickly a bag dries out in the sun hung up on ski poles, skies, a dry rock, snowless tree branches...
You want to be very careful with wearing alot of insulation inside a sleeping bag. I tried that with booties once and they were soaked the next morning and frozen 10 minutes after taking them off. Then they got a free ride in the bottom of the pack for the rest of the trip. Anything you wear inside the bag you will need to wear outside the next morning until your body temp dries it out.
Synthetic insulation works when wet not frozen.
I am a warm sleeper as well I take a WM 5 above bag down to -10F with expedition weight base layer, thick wool socks, and a great hat (don't forget the hat it does wonders for microclimate). It is very easy to dry out base layers while you are putting your boots on in the morning.
My layering this winter is going to be VBL pants, shell pants on the bottom (puffy pants in between when resting), and VBL jacket, synthetic zip up, shell jacket on top (puffy jacket under shell jacket when resting). My hope is that with vbl clothing I can wear all of this inside the bag down to around -20F. We shall see.