What IS "Hunk-o-Seedlings"?
It's how to transplant your seedlings when they've grown very close together.
You can sow as many seeds as you want into a flat, that's up to you....if you don't like thinning seedlings then sow lightly, otherwise you can sow heavily. I am heavy handed when sowing seeds and I always sow plenty. I just thin the seedlings as I transplant them, often I just take a flat and pry off a "hunk-o-seedlings" and divide it into small clusters and plant those as is. When they grow larger I'll thin them out if needed. Mother Nature is very helpful with this too....she'll bop off the weakest seedlings in the cluster so only the very strongest do survive....so thinning is rarely ever neccesary.
OR...if you really-Really-REALLY want to divide those little seedlings into individuals before you transplant them:
To separate any close seedlings just simply take out a cluster of them from the flat, not a big hunk, maybe a piece of soil an inch or two across, and then carefully work the soil loose from the roots to separate them out. To me the action is very similar to butterflying a piece of meat....I just carefully work the roots apart repeatedly opening and halving the soil hunk (this is not something I do when I am hurried or have "anxious" mangling fingers) and I do very little, if any, damage to the roots.
PS....I really personally prefer the hunk-o-seedlings method best. With Winter Sowing you WILL have a gazillion seedlings so planting them out "en masse" will save time, energy, and sanity.