Need Help With 1st Sump For 180G

[Intent]

After looking to trying to find a replacement canister for my failing FX5 I'm really considering setting up a sump instead for my 180G (6x2x2) display tank.
But when it comes to sumps I really have no idea so I'm looking for help.

I've got a 4x14x18 tank spare here that I would like to use.
I'm thinking of using this sump design;
[Not to 100% scale]

From left to right, chamber 1 is mechanical, 2 is biological media, 3 is space for chemical filtration if needed and 4 is for equipment.
The dotted lines are egg crate.

The only real requirements I have are that it can fit a 300W Jager heater and is relatively silent as it's in the lounge room of my house.

I going to be drilling 2x 1inch overflows in the back corners of my tank. But how far from the top of the tank should they be?

I can do the plumbing required no problems but my main issue is the baffles in the sump and how high the egg crate should be. Can someone tell me (or edit the sump plans) to show how tall and far from the top/bottom the baffles and egg crate should be?

For the return pump I'm considering either the Eheim Compact+ 3000 or the Compact+ 5000, both have adjustable flow. (I'm in Denmark so my options are limited)
But I'm not which I should get? I'd like a decent amount of flow with 2 returns.

Many Thanks......

 

[Rayne]

I'd highly suggest looking into filter socks for your mechanical filtration. Much easier to service than those sponges.

 

[Intent]

I'd highly suggest looking into filter socks for your mechanical filtration. Much easier to service than those sponges.

So I would just run filter socks in the 1st chamber with no other mechanical filtration?

 

[gangster]

I'd highly suggest looking into filter socks for your mechanical filtration. Much easier to service than those sponges.

x2

And no need for chemical. Just add more bio.

 

[Rayne]

So I would just run filter socks in the 1st chamber with no other mechanical filtration?

Thats the idea, yeah. I just bought 5 sets of socks and every 4-5 days I take the dirty ones out of the sump and put a fresh set in. When I am down to my last pair of fresh socks in the sump I throw the other 4 pairs in the washer with a little bleach, hot water, extra rinse cycle, and their good as new.