OK here is an example of a simple sump I built for a 72 Gallon bow a couple of years ago:
And here is a picture of another a little more advanced sump I did for another AA member:
And finally a super large more complex system I did just recently for a local residential application:
As you can see sumps range from simple in design, Like this:
To very complex in design, like this:
You are going to have to decide on a design that suits your needs.
What are your goals for the tank? Livestock choices? Reef? You should probably decide on a skimmer and return pump first. This will enable you do design and build (or have built) a sump that exactly fits your design.
As for the overflows, I can't really help you there. I don't use siphon overflows nor do I recommend them to my customers. Not that there is anything wrong with them I just prefer a drilled tank.
So, once you answer the questions above we can try to help you decide on the equipment you need and help design a sump for you.
Is there any chance you could post a picture of your tank ans under the stand?