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Not sure about the forsythia but I would transplant the gardenia to a bigger pot as needed and only plant gardenia in the ground if confirmed that this cutting's parent can grow in z7b. Many gardenia cultivars do not perform well in z7, even those advertised winter hardy to z7. My z8 ones fairled poorly until I switched to very hardy cultivars. If ok to grow outside then plant them in Spring 2022 once the chance of frost has passed (last week in April for Greensboro). If not, grow in pots and bring it inside once overnight temps are below 50°F. Forsythia is more winter hardy than gardenia so a cutting may perform better but make the choice depending on how developed it is at the end of the summer. If the forsythia cutting is not much developed then keep it potted inside during winter and plant it outside in Spring 2022 also.

You can move it from the ground to a flowerpot and vice-versa but may I recommend not doing it in the middle of the summer? The root system is small and shallow. The plant is very sensitive to sunlight changes in its environment. Expect it to complain by yellowing eaves. Your average date of first frost is the last week in October so consider that when moving it. Also be careful when fertilizing with a 90-day slow release fertilizer. Bring the pot inside once overnight temperatures are supposed to go below 60°F. Bring it outside once overnight temperatures are safely above 60°F. Put the pot in rollers to help move it easily and buy an extra set of rollers as a back up in case the rollers break when they are not well stocked in garden centers.

If the coffee grounds are used, they aren't adding acidity to the plant but they do improve the soil's tilth. Just add them occasionally. Here are care tips for gardenias and also info about coffee grounds.

https://www.gardeningknowhow.com/ornamental/flowers/gardenia/gardenia-plant.htm
https://www.gardeningknowhow.com/ornamental/flowers/gardenia/common-gardenia-diseases.htm
https://www.gardeningknowhow.com/ornamental/flowers/gardenia/when-to-prune-a-gardenia.htm

Yes, that is a forming seed pod. You can leave it if you want to get seeds from the plant, or you can prune them off if you want to focus on growth.

Here are some articles that will help you to care for them:

https://www.gardeningknowhow.com/gardenia

Not sure but Gardnia leaves are very photosensitive so they may be orienting towards the sun. Gardenias grown indoors should receive at least 6-8 hours of direct sunlight through a sunny window. Make sure your Gardenia soil is moist and well-drained (keep it away from drying air vents).

Sounds like it is adjusting to less sunlight. I put mine in a southern facing window only in the Dallas area. They will yellow out easily but will generate new growth in spring. Do not let the soil get dry! And watch out for drying air vents.