Re: Which diameter in the tank?
...I don't know how regulate the flow between the tank and the sump! Which diameter do I have to hole the tank?
Generally speaking the bigger the drain the better. The bigger it is the more efficient it will be and the less chance of flooding or noise problems you will have. You want to regulate the flow by the size of the pump you use, not by the drain. The drain should always be able to handle more than your pump can put out.
Which pump does I have to put in the sump?
Not sure what you mean by this.
How many times does I have to filter saltwater in the sump per hour?
There's no hard and fast rule on that, and I have never seen any rule of thumb either. It depends on the type of tank and filtration you are using, whether or not you are also using closed loop type circulation in addition, etc. You need to move the water at least fast enough to remove the scum from the surface of the water, and to provide enough flow to keep your equipment (such as heaters, chillers, skimmers) working efficiently. For example, if the water isn't passing the heater often enough, it won't be able to keep the water warm enough.
Personally, I use a lot of flow through my sump because I run a low nutrient, bare bottom system which follows the philosophy that you need to remove the detritus from the main tank as quickly as possible. The higher flow through the sump the faster the detritus is removed. I've had a lot of success with this methodology - and it's a whole lot less work than others I've tried. I'm running about 2000 gph through my current sump.
For more info on the system I described above, check out
this thread. I warn you though, it is very detailed.