You really need teeth on overflows because any small fish that gets to close will be in your overflow or sump constantly. They don't create any noise, the noise comes from the water level in your overflow. I have not built my 300 yet, just haven't had time yet. Not sure what I am going to do yet for my plumbing.

I changed my mind about the whole thing.. im bringing back the tank i got and will buy a predrilled with corner overflow in it . It's cheaper and i really didnt need the lights ,heater and stuff that was coming in that "kit" i got. I'll chip in 20$ and I'll get that 55g with a 30g tank to build my sump. Would you advice me to drill the sump for the return line and get an external pump or just run a pump in the sump?

That sounds like a good plan, as for return pumps the submersible pumps are good and are reasonably priced. It depends on how much flow you want in the tank from your return. they do have there down side though, some pump can create alot of heat and depending on if you are going to run any media reactors with smaller submersible pumps they might raise the temp in your tank. Just for an example I have a total of 6 pumps running my 165 gal, 3 of each internal and external and my heater has never been on in almost 2 yrs, I actually have to run a chiller.