I just don't want any issues with roots damaging the house or foundation. I have a retaining wall about 4 feet wide, 10 feet long. I planted several holly bushes (4) before I knew how tall they'd actually get. They are still quite small, about 18 inches tall, but I know they will be quite tall.

I worry about root size as I don't want them to have roots that push up againt the building and damage something. They are blue boy/girl holly. Thanks!

Their roots should be fine. They will not damage your foundation.

They do prefer part sun. Best if shaded from direct sun light in winter. Avoid planting on the south side of a building. This latter is very important to the long term viability of these plants; they will struggle and fade in this elevation. No special needs as to soil or watering requirements. You can prune at any time. No serious pest problems. They are drought tolerant once established.