[DJ88]

OK.. before anyone else brings it up.. Make sure you have a well built and sturdy stand.. Been there done that trip.. Didn't want the Tshirt.. [img]images/smiles/icon_biggrin.gif[/img]

I like to err a bit heavier so I usually say 9 lbs per gallon of water or even 10 for ease of math. From there add in your LR(once again I err on the heavy side and dont' subtract what I "guess" the displaced water was that I had to take out for the volume of rock.. For the sump I just figure out how much water will be in there.. as it won't be completely full. Any sand being added.
That will give you a very rough guestimate. But I would much rather err on the heavy side. You know it will be lighter but.. Peace of mind. Plus the additional weight covers equipment.

If you want to you could place a sheet of plywood under the tank that has a larger area than the footprint of the stand. This will take the weight of the tank and distibute it over more of the floor. Putting less pressure on your floor. [img]images/smiles/icon_smile.gif[/img] More peace of mind. Only thing is you have to hide it and make it so the clumsy people(who will invariably come to see your tank) dont do a header through the glass. Now that would deserve a Darwin award tho.. [img]images/smiles/icon_biggrin.gif[/img]

As for the skimer in the sump I think it will depend on the style of skimmer. I have my PM skimmer outside of the sump. If you have the space by all means.. Go for it.. Less chances of something breaking and spilling.

Things I have heard of where water gets out of tank are powerheads aiming up and away.. Overflow boxes losing siphon and the sump being emptied into the main tank and over the top. breakages. If you make your stand concider making the bottom of it in such a way that it is a basin of sorts. and seal it with marine paint. If anything leaks below you can catch 5-15 gallons or so.

I am sure there is more.. lots.. those are what came to mind..