Quick question, so I built this thing and one of my seeds emerged!

It is about half an inch long, with a root sticking about a half an inch from the bottom of the rapid rooter plug. I would appreciate a bit of help from someone who knows what they are actually doing.

1. What should I do now? I know I still need to keep it within the rapid rooter plug for about 10 more days at least until it is healthy enough for a transplant, however how do I ensure it grows? The way my house is positioned dim lighting is hard... I can put this over my 150 watt HPS or a small 20 watt florescent, however I noticed if I do that the rapid rooter get dry really fast..

At what point should I put the humidity dome on?

Thanks in advance!