You are best off getting a new drier, typically they shouldnt be left open, as the dessicant inside can only hold a tiny bit of moisture, and leaving it open will take care of that, this is just from what i've been told on that section of things. They are relatively cheap. After replacing that it would probably be best to replace all the O rings you can, since its open and you want to prevent possible leaks.

Put it all together, go to autozone, they have the vacuum pump in rental tools, pull a vacuum on it, leave it overnight, make sure it hasnt leaked down, then you'll know if thinks are sealed up without wasting a bunch of refrigerant.

Once things are sealed up and you've vacuum'd it, go ahead and fill it using gauges, you should be able to find out how much the system is supposed to hold, should still be the same as stock S14 originally.