Fish-
While thos aspects do add cost, because of the size of the order B6 placed, you gain significant economies of scale. For example, even if they bought 318's, B6 has to order tires for all the airplanes they have. Because the 190 fleet will be sizable in a short period, the price of tires, on the aggregate will be approx. the same as if they bought 318's. While this is a general exmple, this is how a typical fleet planning group looks at this decision.
As for problem recognition, I think it is fair to say that won't be a problem. As is seen at all of the legacy carriers, mechanics can work on multiple types of aircraft. On top of that, the use of manuals, etc. is encouraged, thus making it less of an issue.