You don't want that much intake. It's not enough negative pressure. You're like I was and looking for the easy way out cause you already did the work and mounted that fan twice right? But the thing is you want it done correctly. The most I'd use for the intake, if you feel you must use one (because as I said
you don't need one) is the 160+ cfm fan. What would be better for you to do is to use the
160+ and the 420 cfm fans BOTH as exhaust and a passive inake. The only reason before I said to use an intake is because it was such a big difference (160 - 420). Seriously man just trust me on this, do it the way I said to and you're room will work out nicely.
As far as smell goes best thing you could do is set your room uo the way I said, and attach a carbon scrubber to your exhaust fan. They're really easy to make yourself. I'll try to find an article or video for you but that's the only thing that's gonna take the smell out.
The seedlings are looking nice and healthy.