I don't know why you guys are recommending the photon torpedoes for the aft slots, the Defiant always had quantum torpedoes fore and aft.
Yes, I know that the aft torpedoes looked like photorps in 'Paradise Lost', but they were never referred to as photorps, always as q-torps. Hell they were never consistent with the vfx for the forward q-torps anyway. In 'Defiant' they were blue, in 'For the Uniform' and 'Sacrifice of Angels' they were blue, but in 'Rules of Engagement' the forward q-torps were yellow/organge like photorps looked on later seasons of TNG and DS9, and they were the same in another season four episode, 'Shattered Mirror'.
BUT, regardless of the colour of the q-torps, they always
sounded the same, and they
never sounded like photorps do. There's a distinct difference in both sfx.
As for the other weapon selections, I have quad phasers for my Defiant (I too shelled out for the Sao Paulo class), forward and aft q-torp launchers (one of each), and I initially had beam arrays. But the thing is, the Defiant's beam array had at least one 360' arc. You can see this in 'Shattered Mirror' a couple of times. So I dunno, maybe having a forward beam array with an aft beam array fits, but I kinda wish we had beam turrets.
As for the layout, I kept everything default since that looked right. For the Boffs, if you are going to have beam arrays instead of turrets for that canon look, then perhaps have FAW1 instead of the TS2. Because the Defiant never did an Enterprise-D style torpedo spread, but 'Shattered Mirror' shows the Defiant spam beam attacks when it was close-in to Mirror Worf's Negh'var. I'd recommend HE2 over ST2, not just for gameplay reasons but because ST2 sounds antithetical to the Defiant's approach to things, while HE2 lets it tank more, which is DEFINITELY a Defiant approach to things.

By that same token, I'd have ASIF1 instead of RSP for the same reason as the poster above me stated: the Defiant rarely did any 'tech' solution to tanking damage, it always relied on its ablative armour. And ASIF1 is in line with that philosophy.
I too have ablative hull armour eng consoles and I slotted in the cloaking device here as well (whenever anyone on the show talked about the cloak it was usually O'Brien at his eng station). For tactical I just put in phaser relays, since the Defiant's cannons are supposed to just bulldog their way past any defences.

EDIT for science I put in my Enhanced Plasma Manifold and a Field Generator, but I dunno what would fit in here. Probably not a biofunction monitor though, Bashir complained about the Defiant's lack of proper medical facilities in 'The Search part 1'.
Cool idea for a thread btw
EDIT2 Also, get the Belfast bridge off the DS9 bundle if you haven't already (or if you can afford it). I got it during the recent 15% bonus to zen and I'm quite happy with it. I only wish I can dress up all the ship's crew in the DS9/TNG movies era uniforms.