Wow sorry didnt' know this thread had been so busy
A 29 does have thicker glass then a 10g ,, for that matter a 29 has a lil thicker glass then a 20Long or atleast the ones I looked at. I went with a 29 cause of the thicker glass and its a lil more room for corals,, The 29 is connected to my 72 so I have frags and other corals in the 29 that I no longer have room for in my 72gal.
You would for sure want a 20gal for a peacock, They are pretty big
Luckdown,, I know how you feel. I love mantis shrimp too haha but I do keep an Eye on this one when I have my hand in the tank.. haha,,, I'm getting use to him now though at first I was a lil jumpy He learned I ment food pretty quick and has no fear of me what so ever. He comes up and graps the turkey baster, tongs anything I have a hold of. Just tonight me and my son fed him a molly "feeder fish" and he swam all the way to the top of the water and popped splashing us both lol. I closed the canopy

Just plain awesome
BTW MarLooney is right they will use the hunting room

Helps the prey last a lil longer haha