I have kept mustard and other seeds longer and they still germinated up to 5 years. Some germinated after 8. Proper freezing should allow them to keep longer. I usually do not sow seeds with fertilizer. Too much nitrogen at the start may prevent germination and promote dampening off. I usually fertilize after the seeds come up or I use osmocote slow release in potting media before I plant. In the ground I only need a small amount of nitrogen based on my soil test so I add 3-4 inches of compost, sometimes I add composted steer manure if I have it but I wait 2-6 weeks before I plant. Otherwise, I just add compost before planting and fertilize with sulfate of ammonia as a side dressing after the true leaves have come out. I also plant Asian cabbages after corn as a scavenger crop to scavenge any left over nitrogen.
You can test germinate seeds on paper towels to test their germination rate.
Most of the time. I start my seeds in community pots. For me they take up less space than plug trays and I have trouble with plug trays either drying out too fast or staying too wet. I usually get empties in plug trays which take up a lot more space than a community pot and I don't have problems transplanting out seedlings. I lose a few, but most survive.
If you are planting in trays or pots, make sure your media is damp first, not soggy but not dry either. Seeds don't need fertilizer so either use a slow release fertilizer in the sterile potting mix or wait to feed your seedling after the true leaves come out. The seed has all the nutrients it needs to support the plant until then. I tend to ignore planting depths for most of the seeds I plan to transplant anyway. I surface sow almost everything since most seeds need light to germinate and I have better germination with them on the surface. Larger seeds like sunflowers, I will cover lightly. I only cover seeds that like to be in the dark. P.S. my seeds are started on a bench in the sun. I don't sow indoors under lights and my bench is exposed to sun, air and wind so 4 inch pots work best for me for starting seeds. I do have to cover the trays to keep the birds from eating the seeds.
Mustard seeds I would sprinkle on top and press them in but not cover with soil. I do water my pots daily because seeds cannot be allowed to dry out.
https://soiltest.umass.edu/fact-sheets/ ... emediation
Happy gardening in Hawaii. Gardens are where people grow.