re: Which areas of "Greater Dallas" should I avoid at ALL costs?

In order based on what you have said. These would be mid 6 figures houses on the small side.
MStreets
Lakewood
Lake Highlands

Then go up to plano and Allen. Lucas is great too once you get up there... Prosper is too far.

I commuted from Allen to downtown for 18 years...that was an hour at rush hour. Problem is once you get past the first three above my experience tells me you might get a 30 minute commute 5/7 times in the early am. 1/7 in the afternoon if you are lucky. Great places to live all around though. PS. No to mesquite.