My first question, having a limited amount of experience with kilns, is how hot the hose will be getting? Depending on the temperature, a window vent could melt.

I would probably just use a simple aluminum exhaust vent though the building envelope. You can put some metal caging around the vent to keep animals out. Usually you’d also have a backdraft damper to keep air out too.

Typically vinyl siding will have a much lower melting temperature than electrical wires but I would as you say keep them separated. I wouldn’t want to make a lot of work of hanging the hose up every time.

One thing to note is that flexible ducting provides vastly more air resistance than solid ducting, so if you’re making a longer run and/or have a few bends, it may be worth considering.