I think all onions grown from seeds can be bunching onions or scallions. If and when they mature will grow onion bulbs. It is the same for planting/growing from sets. The difference is that sets will be bigger when they come out. While with the seeds it will take couple of months perhaps to be the same size as sets.

Onions are not meant to be perenial, because when you pull them up as green or pick the mature onios, it will be the end of it. So, one seed or one set (tiny onion) will grow just one onion, no more. Obviously then, it does not make sense to plant a regular onion to get just another one like it. The sets are actually scallions pull up and kept for replanting.(You can actually plant store-bought scallions. Just cut the green part off, eat it and plant the remainder root)
Right now, I have bought some yellow sweet onion seeds (Ferris Moore?). I am going to plant them almost like grass (closely packed packed). As they get bigger I will keep thinning (use the green as chives, scallions) Then when they are about 2" apart I will let the rest to taay and become onions. You can also plant seeds in trays and then separate tyhem and plant them in your garden.

To my experience, onions are very good gardening produce, as you can store them for months and continue enjoying them. I will alo be on the look out for sets and in-expensive pearl onions to plant in December or january (I am in zone 8 GA)

By no means, what I wrote should be taken at its face value. I could have been wrong in part. So, keep reading other comments as well and sift them hrough.
Cyrus

There are several types of bunching onions you can buy to make a "perennial" onion patch. Because the bulbs multiply by division at ground level, the patch will continue to replenish itself year to year as long as you don't harvest all the onions at once! The two types you mention fall into that category. Southern Exposure offers more details on growth habits (link below).

I am also hoping to try some of those next year... I currently only have Egyptian (aka Walking) Onions, which work well for a "perennial" bed. They multiply through topsets; you can break apart the bulblets and plant them out like onion sets to quickly establish a nice patch. Egyptian Onions are generally used as green onions. You can harvest any time during the season... new greens appear each spring as bulbs break dormancy, and continue to grow all summer... then you get more new growth in late summer as the topsets root and begin to sprout. The bulbs are strong-flavored but I like them, and tops have typical green onion taste.

Here is a link that might be useful: Southern Exposure - Bunching Onions

"Bunching" onions are available as two distinct types. The perennial form is Allium fistulosum, which divides into a clump of small onions. All you have to do is divide the clump and reset every year or so. The other type is Allium cepa a biennial. This one grows like a regular onion but does not bulb. It is grown for the leaves and stalks. Commonly sold in bunches , hence the name. Does not divide, one seed one onion.
Topsetting onions (Allium x proliferum), of which the Egyptian Walking onion is the most prevalent are virtually an indestructible perennial.

Another point not yet mentioned is that you are far north - Idaho, right? That means long day varieties only if you want type of bulb formation.

Perennial beds work well this far south but I'd be surprised if any variety could grow as a perennial that far north given the hard ground freeze but it never hurts to try. Good luck.

Dave

I have missed onions make it through the winter up her all the time, but we put a foot deep mulch of leaves on the garden every year. And of course the asparagus, herb and volunteer potatoes do well up here.