(humor)
In a typical data center, the management port would be connected to an out-of-band network that's separate from the data networks. This management network would either be in a different VLAN or a separate physical network.
It depends on what you might get available at a reasonable price... I'd say something along the line of the Haswell family for Intel server CPU (or, if you prefer, the Xeon E3/E5/E7 v3).
The 6450 keeps the same 30%-ish PWM on the fans until inside it reaches 64°C... or just about always as those things consume very little power. As you would call this fan level "silent"... well, it's up to you and your specific item... some will come with louder fans than other. Mine is everyting but silent, even at the low speed.
They definitely have a different power draw, but most likely marginal. Page 6 of this pdf gives you an idea.
I'm biased on this and I know some here have had very different experiences, but I'm really not a fan of the VDX series. The team that was responsible for them at brocade seems like they had the totally opposite outlook versus the fastiron/ICX team. Nearly everything including the ports are locked down with licenses (which I nor anyone else I know can get), the CLI is weird and does not vaguely follow cisco conventions like the ICX line, etc. They're now also owned by Extreme, so you're not gonna be able to get firmware for them. Finding someone with an Extreme support contract won't even be enough, Extreme's downloads are so locked down you'll need to find someone with that exact VDX model under contract to get access to it's firmware. They're also missing some misc l3 stuff like tunnels (VDX will do L3, but the target market was big L2 fabric, so expect some misc L3 stuff to be missing or wonky). Last time I used them they were also vendor locked on optics (again, total opposite design philosophy versus the ICX line), but this could have changed in recent firmware after they got acquired by Extreme.
95f might be pushing it, even with an exhaust fan I'm pretty confident your attic will be well above that, but that said you could give it a try, especially if days like that are rare. if it gets too hot it'll shut itself down, I would just keep an eye on the temps
They have to be the same model, but port count and PoE/non-Poe doesn't matter. EG all ICX6610 models can stack, all ICX7150's can stack
you need to factory reset the switch you're introducing so it's clean, then follow brocade's docs Replacing traditional stack units
you can open it up and physically reverse the fans, but I would expect less airflow this way than just leaving it stock upside down (in my experience intake fans need to run much faster to achieve the same airflow as exhaust fans in these switch layouts), I would test each way