Just wait till all the cold weather is gone and no more cold fronts will be coming through that make the temp drop below 45F , Like the post said before. You can just keep them in the window seal or put them under your CFL at night, but is not necessary if 18hrs of light is received in the window. So keep an eye on the weather forecast in your area for the next month or so and when the temp. is right, put them outside.
Also, when you transplant them outside you can put them in direct sunlight since they sat in that window seal and got used to the light, but they will transpire water out of it and dry out. I use a Transpiration spray called "No Wilt". It locks the moisture in the plants so the direct hot sun will not dry it out as fast. Check them the first couple days to make sure they make it outside alright and then let nature take its course, with of course a little help from you along they way.
And lastly, the north facing hill is not the ideal place to do it. You can, but will not produce to its fullest. South facing hills or plots are what you want. In the northern hemisphere, the sun will move southward in the sky as the year progresses on to fall. So if you plant on the NORTH facing hill you will lose a good amount of light right as they start to bud. My theory for spot picking is an opening that allows the sun to come through from 90 degrees (sun directly overhead) to 45 to 55, or so, degrees and south facing.
The yellow plant, i agree with you on the Nitrogen deficiency. Maybe a mild fert. with high in N, every other watering for a little while til in goes away, if it worsens, then that's not the problem and you will have to try something else.
But good luck and remember to post pics along the way.