I recommend that you do not attempt to build a stand until you figure out the filtration system you are going to use and where you are going to locate it. I know you want to get going on this project, but it's a mistake to start building things just yet. This is a weekend for reading. (See my previous post)
That is correct. Trying to drill tempered glass will shatter it.
Assuming you have a tempered glass tank, the only alternative is an external overflow. IMHO the only one worth spending your money on is the Lifereef ore-filter boxes. See them here (offsite link) -
prefilter box, siphon box, overflow box, siphon overflow, Eurobrace, Euro-brace, Euro-tank
Avoid the CPR overflows sold by many online vendors. They have many inherent design and manufacturing defects, and they are very prone to cause floods or otherwise fail.
A refugium usually doesn't usually have bioballs. What you are looking at is more likely a trickle filter. They are not generally considered a state of the art way of doing things. They do work but they have some limitations. Ask yourself why is it only $100 and why was it never used?
Depending upon exactly what it is, it could be a good deal. It could also be a complete waste of money.
One further thing about equipment. Always buy top quality equipment. It will last, and you will not have any problems with it. This doesn't mean you need to get the most expensive. There are often less expensive alternatives that are sill top quality.