Q.ocean spray
I live about 100 feet from the ocean. Will the lilacs thrive that close, or will I battle with mildewy plants.

Powdery mildew strikes lilacs during hot, dry weather. Your bigger problem is going to be salt spray and possibly high salt soils. Lilac does not tolerate salt. Every state extension service puts out a list of salt-tolerant plants. Here is the list from Virginia:
http://pubs.ext.vt.edu/content/dam/pubs_ext_vt_edu/430/430-031/430-031_pdf.pdf