While you have active krausen you could really just leave it open. When is slows down, a sterile piece of aluminum foil on the top will work. The beer with have a layer of CO2 over it and will protect it. If you are going to leave for an extend period I would get an airlock on it.
I have had really good luck with WB06 with my weissbier. It is very temperature tolerant so easier to keep the banana flavour down and find it gives a subtle clove note. I would second the addition of Munich. If you want stronger banana notes you need to ferment at a higher temp.
It is in the head space of the bottle). It is reabsorbed into the cider as the temperature drops. Cold cider should have more CO2 than warm cider. You should be safe as long as you raised the temperature of the cider to 180.
I have had really good results with Saf WB06 wheat yeast. Nice clove flavours and no to little banana. Does well holding this flavour even at higher temps (high 60s to 70ish).
Agree, give it time. You can move the bottles to a warm room to help speed things along. I have had batches where I have under primed, but with a little extra time they have been fine.