false wall

what type of false wall do you mean? There are some ceramic walls that satnd in the back of the tank.
Well, I order them pre made cuz I find routing teeth to be one of the biggest PITAs around. I get them made from firstclassaquatics.com, barraquatics, and right now I am having Myreefcreations make a few. You use 1/4"-3/8" black cast acrylic...tell them where to cut the teeth, pay them $30-40 or whatever, and when you get it in the mail...use silicone to glue it in. Now, technically, silicone wont hold plastic like it does glass...but in this case...the pressure on both sides will be rather close (the water in the sump section will be what...2-3" below the other side?) and the plastic wont go anywhere.

I dont have themdrill the holes for piping and bulkheads however. I wait until I get it, then plan out my plumbing, and drill the holes myself with a hole saw...on acrylic its simple enough.
I do all my tanks under 60g like this FWIW...I have 2 of the 40s, a 15L, and a 45XL with what I like to call...'integrated sumps'. They allow me to completely cover the tank with glass for less evaporation (except the 40 with the 250watt halide over it), eliminating the need for an ATO, and other costly equipment that isnt always that reliable.

The hardest part has been equipment. Space is at a premium with an integrated sump. I end up DIYing my own skimmers and chemical chambers to fit into the chambers, and find myself leaning towards T5 lighting more and more because it can be used with a glass top...good luck doing that with halides.

The greatest benefits have been...
1. low/no noise (no overflows/drains/sumps)
2. much lower electrical sonsumption & heat (an integrated sump requires only a powerhead to work the overflow)
3. less evap (and humidity in the house)/ no need for an ATO with glass covers and T5 lights
4. no leaks, costly overflow plumbing/return pumps, etc. The tank doesnt have any holes / pipes and is completely self contained so leaks/ overflows are not an issue.
If your flow into the sump area is not going to be that high, you will want to skip the teeth. Teeth reduce the amount of surface skimming by a very significant amount. They seem to be one of those popular "must haves" that in many cases are simply useless at best.

you can skip teeth, but you will need some way of keeping critters & fish out. Either a slot baffle for the overflow, mesh, or something. Considering I am from the 'low flow' sump camp, teeth dont hinder much since I keep it pretty low capacity and use the false wall to hide additional powerheads/closed loops/etc.
If your from the low flow sump camp... then the the water over a flat overflow is not likely enough to allow critters into the overflow.

I put 1500+ GPH over a 4ft flat overflow. The only critter that ever ends up in the overflow is a cleaner wrasse. However he would make it through teeth easier then what he does now. Snails come and go out of my overflow area.
If your linear OF length is appropriate for the flow your looking for, the teeth will not impede your OF too much. Use the calculater on the homepage to figure out how much OF inches you need, and work from there.
Matt, you may want to rethink your understanding of linear overflow and teeth :)

The teeth will impede the surface skimming by AT LEAST the sum of their total linear length. Teeth will not "impede" the flow now matter how small or few they are. The less total linear opening in the "castle wall" the deeper the flow through each tooth. The more open area, the shallower the water and the better the surface skimming. The "FLOW" is determined by the return pump, not the teeth.

I hope this makes sense. Again, the linear overflow calculator on the RC homepage is for the purpose of determining surface skimming, not capacity of the overflow. Adding 30% closed area to an overflow in the form of solid teeth, will reduce the linear overflow length BY AT LEAST 30%.