I had an almost exact idea of making a sump with a similar design to yours. I kind of wish I had a glass tank vs acrylic now because I have never had to weld acrylic and I'm afraid of messing up the baffles on the sump. I will have to bite the bullet though and give it a shot.
I had planned on making a drain dump section exactly like yours with an overflow in to a filter sock section as well. Is that second baffle from the left raised? I really can't tell from the pics. I'm assuming it has to be, and it goes by the poret foam. Is the skimmer section where bio media is kept? I really have never researched it at all and I am assuming that is what it is for? If so, I see why I never see media in bags and/or inline within the sump in SW tanks as much.
As for the BA setup, I did plan on getting a full gate valve as opposed to the ball valve, but I thank you for the reminder just in case
. The 1.5" I am looking it is going to be right around $50 which is pricey, but I see the necessity for it.
I found a cheaper gate valve ($24range) but did not want to skimp out on a vital part of the overall system.
Do you have any other tips, or maybe things you would change if you had to redo your sump?