Planted a Salix Viminalis windbreak. Bad decision?

No - you need absolutely proper, full strength stakes for trees. Do you watch Beechgrove? This week's episode had a little item on choosing trees, but it's also got a piece on staking. You'd need double stakes to make sure the trees are sound, even if they're young trees or whips. You can also see articles on staking on Youtube etc. Don't underestimate that part of it.
I think the thing you're describing [metal tube?] is for preventing grazing animal damage -deer/rabbits are the norm, but that may not be a problem where you are. They're usually plastic.
Those plugs will need grown on too, before planting out. You'd need plants that are filling a 5 or 6 inch pot before planting out, to ensure success. You might get away with a slightly smaller size if they're ready by about late July/August, as they'd have time to settle in before colder weather

 

Ah ok! Double stakes it is! Dang, so much to learn, lol. I don't have TV so I don't watch gardening shows, so far I've just got youtube and my Gale Force Gardening book for resources. I'm leaning more heavily on the book simply because the author lives in Shetland and only writes about things that can grow here.

Thankfully the other hedge plants I bought are much bigger and in pots so I should be able to plant those out right away. Those make up about half of the hedge. The other half are plugs, so will pot them up and wait patiently! I'm not one of those patient types of people, which isn't ideal for gardening. Maybe gardening will teach me to slow down.

Thanks for all the advice on my thread so far, you and the others have no doubt saved me quite a lot of money and time.

 

You can watch B'grove on iplayer if you don't have TV. It'll be available for a fair length of time