If you took care to minimize root disturbance, you could probably pot up now with minimal distress to the plant. However, the plant is now preparing for winter and storing energy in roots and cambium for its upcoming rest and subsequent spring growth push. For that reason, I would wait until spring to change containers. The best time is before budswell. Read on for other info regarding over-wintering. Your tree will fare poorly indoors over winter. In addition to the fact your plant will react poorly to indoor cultural conditions, your tree needs a dormant rest period and some chilling temperatures to insure it grows with good vitality in the coming (next) growth cycle. Temperate trees that are deprived of dormancy and the requisite chill that releases them from dormancy either exhibit very weak growth or enter dormancy at extremely unusual times, sometimes in the middle of summer or even during normal peak growth periods. This is usually fatal for the tree. The best place to overwinter your tree is in the ground. Leave it in its present container and bury the container to the rim next to a building foundation, preferably on the north side out of sun and wind. You can also overwinter in an unheated garage, but if you do, the tree will break bud too early. When this occurs, you'll need to move the tree outdoors whenever temperatures are above freezing and back inside when temperatures get near the freezing mark. Allowing the tree to grow in the garage with inadequate light will drain energy and destroy the appearance of the tree unless you prune the weak growth off when you move the tree outdoors, but this is a huge waste of the tree's energy reserves. Al

Japanese maples grown in a container in your zone must be overwintered in a protected location. That means a garage, unheated basement, greenhouse, etc. Just wrapping the pot is insufficient protection - temperatures that drop below around 26F can fatally damage the root system. Otherwise, a lot of Japanese maples should do well in your zone in the ground - zone 5 is generally considered the lower cut-off for these trees but location and/or microclimate can extend that. Look at whatever JM's are available in your area - otherwise, check out some good JM's for colder climates, like in the attached link. Here is a link that might be useful: JM's for a cold climate

Ok, a couple of additional thoughts: 1. In the backyard.... between those 2 spruces, I have 3 black lace elderberries.... 2 years in a row, they died to the ground, but came back. This year, with all the snow cover, they maintained their wood and are leafing out. But this winter, to me, seemed more like a zone 5 winter. 2. If I container plant, can someone please recommend a good potting medium and/or fertilizer regime to keep the tree looking its best?

That's a great question, Gary. Ideally, you would want to amend an area equal to the mature root spread. But it is nearly impossible to guess exactly what that may be - roots do not necessarily grow in a perfect circle and depending on soil conditions, they usually just keep extending over the life of the tree. And very often, that is just not a practical approach in an already established garden. If you feel you need to amend, do so over the largest area you can manage. And to avoid any 'bucket' or 'saucer' issues, dig a very wide but rather shallow planting hole and set the rootball high (above grade). Mound the backfill up to the top of the rootball but not over the top. Make sure the sides of the planting hole are very dished or sloped and roughed up (not smooth). Feeder root will penetrate into the indigenous soil. It is just that if you make the planting hole too rich and appealing by amending, the roots are less inclined to extend properly and you risk them circling around in the original hole rather than extending laterally as they should. Roughing up the sides of the hole helps with this.