Lyn, any clematis can be used as a ground cover plant. Most clematis will attach themselves to any vertical surface and climb upwards if they encounter such a support so if you plant SAC the plant will do so. As a plant matures, it will mound up as new basal shoots emerge from its crown and grow out from the center of the plant. If you want to help the mounding action somewhat, plant the SAC so it will grow over an old stump or even some device you construct out of chicken wire or old fencing.

Whether or not trees in pots that are set in the ground require more attention depends on what you're comparing them too. They require more attn than trees planted out, but less attn than trees planted in containers maintained above ground. You will still get a dwarfing affect with shorter internodes and smaller leaves, but it won't be as pronounced as it would be with a tree in an above-ground container. A good guess is somewhere half-way between normal growth (in ground) and how it would grow under container culture. You would still need to lift the tree & root-prune/repot on a fairly regular basis though, to keep the tree growing with good vitality and close to its potential genetic vigor. A couple of benefits: You'll be hard-pressed to over-water. The earth will act as a giant wick & pull any excess water from the container. You will also gain considerable benefit in the fact that the extreme temp swings associated with regular container culture are avoided because of the buffering effect of the earth. I grow lots of woody stuff on for bonsai. If I get something that's really root-bound in a container, and CERTAIN to decline in the upcoming growth cycle because I was too lazy to repot, I often sink the container in a bed or garden until I can get to it the following year. It's an oft used strategy for bonsai practitioners. Al

I think the confusion is in that root pruning can mean different things to different people. What they are telling you is that if you are digging the plant up from being field grown, you can damage too many roots by just digging it up all at once. When people with field growing operations want to minimize the stress, you cut some of the roots and then a couple of months later, after those roots have heeled in a little, you cut a few more roots. By the third time, you dig it up and only a third of the roots are freshly cut during the actual move. This plant was in a pot and you already cut some of the roots that were going in the ground. That is all the root cutting you need to do. It is possible, depending on how many roots that was, that even that can stress your plant. If I was doing this, I'd cut some leaves. All plants have bottoms and tops and there is a ratio between the two that create the balance as it was growing. The more roots you cut, the more leaves you should remove. That is something only you know the answer to. I'd cut a few of the good leaves myself, just to make sure. they can grow back in time. As it is, after it is planted, if you see more leaves turning brown, you will know you should have cut a few more off. The plant will show you in advance what the balance is.

If you are not going to be planting them until next spring, you will definitely need to heel them in (bury the pots in the ground) for them to survive the winter. Otherwise, they will be need to brought into an area that offers considerable protection against cold weather, like a cool/unheated basement or an attached garage. FWIW, many gardeners that acquire plants faster than they can accommodate them in the garden follow this method of storage until a more suitable planting time, developing dedicated "nursery beds" in an out of the way portion of the garden or a disused veggie plot to house their pot nursery until they are ready to plant them in their forever home.