Personally I would say you are too late now for this year.
I have only grown them from seed a couple of times, and I wasn't really happy with the results.
But then again at that time I wasn't quite sure how to grow them or more to the point when to sow them.
Since then I find planting 'setts' the easiest way to grow them so I don't bother with the seed route anymore.
In fact this year was the first time in many years I have grown 'main crop' onions from seed and I was quite happy with the results. So much so I might have a go at growing some 'large' onions this year.
:o Which makes me think if I am going to do this I will have to be starting up within the next 4-6 weeks if I am going to get any success ::)
This is how I did my Japanese Onions ;
http://www.thegardenersalmanac.co.uk/Data/Onions%20(Japanese)/Japanese%20Onions.htmI don't know what seed sowing facilities you have but it might be worth while using just a few of the seeds you have and grow them like this;
http://www.thegardenersalmanac.co.uk/Data/Onions/Onions.htmWho knows you might have a bit of success i.e. nothing ventured nothing gained!!