I don't grow ficus (figs). So with that said all I can say are generalized strategies for keeping a tender tree indoors. I think the common and Latin for your tree is: a "Moroton Bay Fig" (ficus macrophylla).
While your tree may have spent a longish time in training, retailers of bonsai like politicians only lie when their lips move. Don't wager the life of your new tree baby on it having a large root mass able to overcome the drying effect of heating-air conditioning ducts. Grow him on or near a window sill untill you can obtain lighting for him. Away from drying HVAC.
I wouldn't repot untill your spring rolls around. Please use dedicated soil for bonsai (or cactus) or soil of your own manufacture. Loess and or peat based soil hold too much water for residence in north america. Your tree baby will drown in it.
Ficus shed leaves when light levels or temperature levels change. This is the tree-equivalent of a pee-pee dance, of stress.
Once your minimum temperature goes above 50F it probably aught to move back outdoors, its a tropical, and can tolerate a lot of sun with adequate water.
If you just gotta keep a tree near the desk, get an ivy cutting, it will tolerate living in a people space better than a fig will. And yes, you can prune an ivy into a vase shape.
Think like a tree
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