I can comment on the flak vest and leave the more precise measurements for the armor plates to someone else.
That looks like a MoW vest and in it's current state it is not 501st approvable.
It needs to "close down the back" according the 501st CRL.
I recently brought up the same question on the Bounty Hunter Guild forums. I ended up selling my MoW vest and getting one from Arkady.
I see have may have jumped the gun on my answer. You were asking about the vest in the bottom pic, not the MoW vest in the top 2.
Part of that will depend how and where it closes up.
Without more pics, it's hard to tell, but if you're aiming for 501st I've highlighted a few parts of the ESB CRL that might apply:
For 501st approval:
- Flak Vest has appearance of 'tackle twill' fabric and be light gray in color, weathered and quilted.
- Flak Vest closes down the back.
- Flak Vest has short shoulder tabs to mount the shoulder armor. These tabs are quilted, running from the end of the tab up to the shoulder.
- Flak Vest has slits cut into the back for the jetpack harness straps to feed through.
- Vest allows for the attachment of chest, back, belly, shoulder and collar armor.
- Vest is short enough to stop before reaching the girth belt. It is no longer than necessary to mount the armor (approximately 1/2" of vest shows below the armor).