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It needs to be in sun to produce the intense red color. The more sun, the more color.

Virginia Creeper will not damage the wall, and in fact it is common for people to cover walls on purpose with this plant. This article will help: https://www.gardeningknowhow.com/ornamental/vines/ovgen/covering-brick-walls-with-vines.htm

Although it prefers to climb, it will, most certainly, cascade down the retaining wall.

Virginia creeper does not dig into tree bark so it does not directly harm the plant. If it is allowed to grow unchecked, there are 2 potential problems. The leaves may block sunlight to parts of the tree which may cause shaded needles to decline; and a large creeper vine can girdle the trunk but this is not common. Cutting the vine every few years will keep the size manageable and safe.

Normally over time, these will attach themselves. They have a tendency to climb anything available. If they do not, then you may have to find a new place where they can climb.

Most vines, except for ivy, and some types of forsythia, will die back and will need to be cut during dormancy. But those two can be an evergreen in your zone. You may also try creeping junipers trained upwards.

Here are a few articles that will help:

https://www.gardeningknowhow.com/ornamental/vines/virginia-creeper/virginia-creeper-maintenance.htm

https://www.gardeningknowhow.com/garden-how-to/gardening-by-zone/zone-7/zone-7-junipers.htm

Forsythia shrubs can be trained into vines: https://www.gardeningknowhow.com/ornamental/shrubs/forsythia/forsythia-shrub-care.htm

https://www.gardeningknowhow.com/garden-how-to/gardening-by-zone/zone-7/zone-7-junipers.htm