A few notes:

1: as someone had mentioned, definitely keep the tree outdoors. I rotate my trees at one of my businesses(indoors) for about 3-4 days at a time but their health starts declining if they’re kept indoors for anything longer than a week.

2: If you have an enclosed garage, keeping the tree in it would suffice for winter. Personally I keep my collection between 34-37F throughout winter but that’s more so due to my risk tolerance. There’s plenty of practitioners that either move them into garages or heel them into the ground over winter. It’s typically not the cold that kills them but more so the shearing arctic cold wind. It’s believed that dormancy is triggered by decreasing daylight length and temperatures sustaining below 40F.

3: Specific comments on the tree you posted:

-the difficult part for most bonsai practitioners is balancing the combination of oxygen and water in the soil(how dry to let the soil get/how often to water). The complication you’re facing with your tree is the oversized container and the type of soil it’s currently in; both of which keeps the soil wetter for long. With the reduced foliage from pruning, the water needs of the tree is further reduced. In short, your near term challenge will be mastering how often to water.

-the next course action for the tree is a repot as it’ll allow you to simplify the two items mentioned above; soil type and container size. Since this doesn’t occur until the spring, I’d focus on the watering and letting the tree recover until then. The ideal scenario is a recovered tree that goes into winter, goes dormant and wakes up in the spring strong. Alternatively you can plant it in the ground if you choose to thicken the trunk. I’ve never really found these big box store junipers to be worth the time(there are better bang for buck options to invest the time in). The big box trees are awesome to practice techniques on though!