Is the tree not getting enough sun?
Welcome, Justin.
The sapling (it's a very young plant, you do realize that, no?) should be in one place, no moving around, where it can get morning sun and late afternoon sun, but NO direct sun from 11am to 4pm ideally.
Is "under the porch" bright enough?
If the porch is not as bright as dappled sunlight, then the answer is yes, it needs more sun.
Am I watering too much or too little?
I guess too little; you should water it till water is dripping from the holes of the pot. Just a little water to dampen the surface once a day is not enough.
Should I re-pot the tree despite it being the middle of summer here in the US?
No.
Even if your soil looks too organic, water properly and postpone repotting until Spring arrives. Then, IF the plant is healthy change the soil to a good bonsai draining mix.
Should I add fertilizer to stabilize the tree and bring back the vibrant green colors?
Giving it some fertiliser when it gets happy again is advisable.
I have been using organic pellets (Biogold) and my saplings look very healthy.
Any help or suggestions would be very much appreciated!
Keep it outside, keep it alive.