Hi Chenoa -- you've already been given a LOT of good information, hopefully this isn't just all adding to the confusion.
When I start seeds in cell packs I remove the cover once the majority have sprouted; otherwise I've had problems with the little seedlings rotting. But once the covers are off you do have to check daily so they don't dry out. Ideally (in my mind, at least), once the seedlings have reached a size that isn't too hard to handle they should be moved to individual pots. That said, mine often stay in the cells much longer than that, waiting for me to take time to pot them up; if that happens, be sure to kind of break up the mass of roots to help them continue growing (I just use my fingers to kind of split them up).
Planting calendars can often be quite misleading, although they do offer a starting point, at least. This does seem quite early to me for you to have Brassicas started (I've just recently started some for a fall harvest myself), but at any rate I think the very best way to get the timing right is to start a few plants every week or so and just keep planting... some will have been started too early that way, and some too late, but the others will do well. The timing can vary from year to year, but after a few years of keeping track of your results you'll be able to narrow the time frame down quite a bit. And some things are much more forgiving than others...
The biggest thing is to keep in mind that every year some things will work and some things won't -- enjoy your successes and learn from the failures, and as Rick said you will soon be teaching gardening to the Master Gardeners!
