You usually won't need to put a bead on the inside after the 4 sides are up. The silicone will usually squish between the two panes of glass and when this happens, you can smooth it out with your finger (don't wait too long though, or you'll make a mess of the silicone). Don't worry about the silicone the squirts out on the outside. After it dries, you can just go and cut that stuff off.
Masking tape is definately a good idea. You don't want silicone spots all over your tank! IIRC when I build my tank I did 1/4" or so. It'd be also great if you can get a friend or two to help you out while building it.
Also, make sure you clean the edges with vinegar in case there are any residues on it. Most importantly, make sure the glass is dry!
Good luck and have fun!
__________________
32"x32"x20" Cube-ish tank
|