I mainly use Jiffy pellets the last few years to do rhizomatous begonias by leaf wedges. Canes cannot be started by a leaf though. Some Asian species cane-looking begonias can be started by a leaf such as brevirimosa and amphioxus. I started six Silver Queen wedges (one leaf) in Mid-November and this is what they looked like two weeks ago. I think 3 starters would be ample for this 10 inch pot. I started Mrs. Ludwig early this month and this shows some with roots two weeks later. I now have two that have put out tiny leaves. The green ones are not Mrs Ludwig and neither are the two on the right front row. The stem is Janet Brown which fell off so I saw a dormant bud and am trying to get a new plant out of it. canes are easily water rooted or stuck in soil and watered lightly. This is the pot of canes from above 3 months later.

Bougie, There are plenty of places to get most of the ones you list above. Some you might find locally - check from spring until fall at local nurseries (especially the ones that carry begonias) and the big box stores - you never know if and when a shipment might come in with a few begonias. I've picked begonias up at Walmart, Home Depot, and Lowe's. My local Ace Hardware was one of the best places I ever picked up begonias but they went out of business twice now (different owners). I cited several mail order places in another thread on this forum. My recent purchases were from Accents for Home and Garden, Taylor Greenhouses, and Logees. Prices vary but if only one vendor carries the plant you want then you can either pass it by or pay up. Most plants will be on the small side when buying mail order so treat your new plants like babies when you get them until they get some size on them. Come to a convention if you can manage. It is an expensive way to get plants when you add in transportation, lodging, meals, registration but it can be fun and you will have a ton of begonias to choose from at very reasonable prices (cheap prices really). This year's convention is at the end of this month and is in West Palm Beach, FL. It sounds like there will be over 100 different varieties to choose from plus one trip is to Palm Hammock Orchid Estates which is a regular smorgasbord for begonias.

You have a lot of area to cover. I'd use landscape plugs. My go-to source is The Pollen Nation, which has reasonably priced trays. I would not put a garden around the maple and then grass around that, but put in a groundcover on the whole space. One of my faves is moss phlox. It comes in pinks, whites and purples from pale to pretty bright, is pretty much evergreen and low care. (Of course you haven't said much about your climate). Then, in the moss phlox, I'd scatter a bunch of other perennials and bulbs for 3 season color. If you have the shade, you can do Heuchera as a groundcover, but it will be quite expensive any of the fancy, named varieties. I think Tiarella Cordifolia is a great groundcover for shade. The leaves look a bit like Heuchera and it spreads. But, I don't think you have the shade. This is zoomed in and looks bigger than it is in reality Get Year-Round Good Looks With Matrix Planting in Your Garden (houzz.com)

Yep , onions planted in the fall keep their tops and stay at constant height pretty much till next spring . Then when the daylight gets longer and it gets warmer they grow progressively taller. I've gotten better results by covering during the coldest part of the winter , like during single digit arctic fronts. I've had onions freeze out down in the mid/low teens. I think the thing is "How Long" was it that cold. Onions are pretty tough but it doesn't hurt to cover them during the worst of the winter with either a low tunnel or just mulch / straw hay. My local feed store doesn't get DixonDale bundles in till January so I plant those in the early spring Feb/Mar. But they get in onion bulbs ( sets) in the fall around Oct. They're just generic white , yellow ,and red bulbs. I heard that they're a long day type but don't know just what variety they are. So I plant those in the fall and overwinter into spring and harvest in the mid summer....about 9 months later. They do make a sizeable bulb but it takes them a long time. And some of them will bolt in the early summer , but not all of them . The less bolting , the bigger the bulb. It gives me some extra onions aside from the ones planted in the spring. And they have a sweeter taste than the spring onions , probably from being overwintered and the natural antifreeze .. sugars , that they build up. And they can be used for green onions (scallions) through the winter if you want to pull them then. The bigger problem I have with the spring planted onions is the too wet springs. Onions need a lot of water but not multiple inches all at once for long periods of time. Then I lose a lot of them from rotting in the ground. Okie HU