Well I normally dry hop for the entire time it is in the secondary, and have had good results. I only secondary for about 10-14 days, then cold crash then keg or bottle. Good luck on what ever you decide.
For cleaning i would use Oxyclean, that stuff works wonders. as far as the rust is it in the keg? if it is on the surface is it where it is welded? the welds could have an iron to it to allow it to rust. I myself am thinking of trying these 5L out they look like it would be great to take out on...
+1 on Hercher. that would be the best way. And i two put the lid on and it does seem to help with aroma, again dont know why but i dont have to, lol. :tank:
You could do an Imperial Porter. I have reused my yeasts a few times to good outcomes. There are a couple ways to do it. first you could wash and decanter your old yeast, very time consuming, or just pour on top and shake. IMPO the pour on top works good for me. Good luck. :mug:
I have to second Ohrumphf. Using an aluminum pot is fine i used two in the begining and had no effects. As far as ice i would go with the ice bath and cool it that way to keep from any kind of contamination. you could use 2 litters frozen and sanatize them befor putting them in, i did that befor...