I recently purchased a red navel orange on clearance from our local garden center which was being rejuvenated from an overly humid/moist summer and fungus under the leaves. See picture with little black specks on leaves. The nursery was hesitant to sell me the tree but did so with full disclosure of the issues. (I also purchased a small limequat seen in the lower left corner of the picture).

This is my first time venturing into citrus and we live on the north edge of zone 6 so I have to bring them in for the winter. This bank of windows faces West with the sliding doors on the other side of the tree facing south. The south doors have a balcony above so not much direct light gets through them. Do you think the trees will get enough natural light through the winter to do well or should I supplement with grow lights?

Another angle:

The tree has one little orange on it. Should I leave it to see if it ripens?

Grafted onto flying dragon root stock I believe.

Black leaf spots. This is what the local nursery said was the fungus they were treating. Any idea what it is and should I pull the remaining leaves off of the tree that have it or try to treat it again? The tree appears very healthy other than the spots.

My plans are to repot in the Spring with a good citrus mix recommended on the forums when moving outside.

Current plans are to fertilize once a month with an acidic fertilizer given to me by the nursery and then I ordered liquid seaweed as well which I have given one dose of and plan to use sparingly until I repot unless you have better recommendations. Any advice is welcome including if I should prune the orange tree now or leave it. Thanks!