Most of the people commenting are suggesting a complete setup. This is just one part of a DIY. What you bought will work fine but it requires you to do some of the things that are already done with the full systems.
yes
It will depend on your U pipe. What are you going to use? if you use 2 90's you can cut them down to make them take up less space.
No it doesn't but if you drill to fast it will start to melt and gum up the bit. I find a little water makes it easier or you can just stop and clean the bit if the teeth get clogged. it only take a few seconds.
any kind will work. Harbor freight has a kit with several sizes for around $10.
I would drill a return. The size is going to depend on the return pump. Do you have a pump yet? If so what model.
Yes. Also be aware that the hole size for a bulkhead is different than the size of the pipe that connects to it. BRS has the hole size listed for the different size bulkheads they sell. Other brands I have used have all worked using the size holes BRS suggest.
It would but I would use a hole saw. Also the way I do it is cut a 1/4" piece of scrap the same size as my box. Drill a hole in the scrap the size I need for the bulkhead and in the location I want it. I then clamp this to the box as a guide to drill. Then I move it to the tank as a guide to drill the glass. That way everything lines up.
I would not but different people do things different ways. I gasket in the proper place will never leak. However once installed it should never have to be removed but I would think it would be unneeded.
It doesn't matter but it is easier.
I don't. I just think you need the rest of it.
Not at all.
I bought one of the commercial overflow systems recently. After looking at it and reading some post on it I sent it back. I built my own. So basically you are building your own but your need to decide what you want/need. Mine was for a small 56gal tank. I only need a couple hundred gallon turn over an hour. I used 3/4" return line. No pressure 3/4 can flow 660 GPH. I only used a 1" drain with a backup 1" drain. 1" no pressure can flow 960 GPH. I used 1 1/2" bulkhead going through the tank from the inside box to the outside box. I would always try to build to hand twice what I expect and be able to remove twice as much water as I can put in.
Here is a video and some pictures of a small tank I did last month. It is work perfect for me. I thought of doing a bean but didn't. If I had I would had need to make the outside box bigger.