Hello, I recently purchased a Ficus Microcarpa Ginseng plant from a home improvement store. It’s my first bonsai plant. My question is, should I repot it now in proper bonsai substrate? Or, should I wait until the spring?

Microcarpa ginseng is not a bonsai. Once you have read up on the bonsai hobby you will understand why.

A tree is repotted at the right time of the year and only if it is healthy. For beginners I advice to wait one extra year to get the care right before. I also recomend doing the few first repots under supervision of someone experienced.