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This article should answer your questions: https://www.gardeningknowhow.com/ornamental/shrubs/lilac/pruning-lilac-bushes-when-to-trim-lilac-bushes.htm

Young plants often do not bloom reliably their first few year, so that in and of itself doesn't meant much. However, wilted leaves are a cause for concern. You don't say how far from the lilac the construction is, or if the sodding was done near it. Roots spread out quickly from the bush, and feeder roots are near the surface, so anything that covers the soil (concrete or sod) can interfere with the absorption of water, which leads to wilted leaves. Given some time and plenty of water, recovery should be swift. However, if the lilac was a distance from the distrubances, you might have some disease going on. Here's an article on Japanese lilac disease: http://hyg.ipm.illinois.edu/article.php?id=166
You might also want to take samples to the Extension Service to ask for analyis. This article will help you locate one: https://www.gardeningknowhow.com/garden-how-to/info/what-is-extension-service.htm

Lilac aren't considered invasive. There are many varieties; make sure you know the name of the cultivar you choose, and check the plant tag for size at maturity. If there's no plant tag, get the information from the garden center. Then plant far enough from the wall to allow the bush to mature without squashing up against the wall. Here are some tips for lilac growing: https://www.gardeningknowhow.com/ornamental/shrubs/lilac/lilac-care-growing-and-planting-lilac-bush-plants.htm

The most common diseases of lilac are powdery mildew and lilac blight - this doesn't look like either of those. It's hard to tell from the picture - I only received your third pic - but are the spots on the leaf undersides able to be scraped off? That would be scale insect, and easily treatable with neem oil or soap spray: https://www.gardeningknowhow.com/plant-problems/pests/scale-bug-how-to-control-plant-scale.htm
Also, the fact that the problems appeared after you repotted suggest there might have been something wrong with the soil you used. You might want to access the local Master Gardener organization, who could tell you how to get a soil test done. They have loads of information and assistance available for home gardeners. This link will help you locate the nearest group:

http://mastergardeners.org.uk/get-involved/find-your-nearest-master-gardener/

I would suspect a fungus, possibly one affecting the roots of the plant. Treat the lilac's leaves with a fungicide and then water the ground around the bush with fungicide laced water. Make sure that the drainage around the roots is good and that the plant is not in standing water.

Give the plant some bone meal to provide phosphorous. This will help the plant regrow its roots if there was damage from a fungus.

Some lilac varieties do well in South Carolina. In you case, I think it would be best to visit a reputable local nursery and see what they are selling in terms of lilacs. Small local nurseries tend to sell varieties that will thrive in your area (as opposed to big box stores who often sell the same varieties across the country regardless of what does best).