I've only heard good things about the Montessori school. I'd certainly recommend a visit to speak with the faculty and students first-hand.
As to strong high schools, were you thinking public or private? Wando in Mt. Pleasant certainly ranks strongly as does Bishop England. Not to mention the magnet and other private institutions. For a report on the public schools you could always go to the state website and read through their test scores.
https://ssl.sc.gov/SchoolReportCards/
From what you've mentioned in your post, I think a number of neighborhoods in Mount Pleasant, West Ashley, and James Island might suit your needs nicely. All would be close to downtown, relatively close to the beaches, and still within a short/reasonable commute to Daniel Island for work.