Serving off a picnic tap, carb questions!

I have some apfelwein that is going to be ready to keg next week, and also have a christmas ale that will be kegged in 2 weeks. I am bringing the apfelwein to my gf's christmas party and the ale to my parent's house for the holidays.

Question (these are my first kegging endeavors):

At the gf's, the keg will most likely be left outside the door, I'm in Maine...that is going to mean 30-40 degrees this time of year. I am serving it with a cobra tap off of 3ft of hose. Serving pressure is somewhere around 1psi. I want the apfelwein to be carbonated somewhere around 4 volumes. I will chill the kegs in the basement and put them under the appropriate pressure for about a week. When I get to the party, I blow off the co2, set to serving pressure, and go...how will the keg stay carbonated for the whole night? Or will I have to put it back on the gas? After the party, when I bring home what's left, do I need to put it directly back onto carbing gas, or can I let it sit until i'm ready to drink again? Same questions stand for the christmas ale, which will be slightly less carbed.

Sorry if these are hairbrained questions...I'm just a kegn00b. Thanks for taking the time to read this!

Just like a keg of Coors Light, it will stay carbed under low pressure for a few hours. I think you'll be fine.
As far as going home, I'd hook it back to live gas over night...just to stabilize the carbonation level, then you can unhook and store.

4 volumes? That's a massive amount of carbonation for apfelwein. Unless you've done this before with good results, id go a lot lower.

Thanks Kahuna, exactly what I wanted to know.

Wildwest...I haven't done this before...I believe edwort said he did this in his thread, and served it like a pseudo champagne, which is what I was hoping to accomplish. If the consensus is that it would be messy, I will do something lower. Another question, like I said, I am using a 3ft line...would it make sense to use longer line? and how long would I need it to be to make the serving pressure and the carbing pressure the same?

tnx again for the swift replies!

If you want approx 4 volumes, at 40 degrees you'd be at 29 psi (see the carbonation chart here: Force Carbonation & Carb Table

To balance that, you'd need like 25 feet of line. Otherwise, you'll get a big glass of foam. If you want to go a bit lower, you can probably get by with 10 feet of bee line, like maybe at 15-20 psi. I'm just guessing on that part- you'd probably want to just reduce the psi until you don't get too much foam.