The love story between Heiji and Kazuha is merely identical to that of Shinichi and Ran, so that doesn't really say anything. (Both Shinichi and Heiji's ignorance towards Ran and Kazuha, respectively, is love in disguise; they just have trouble admitting it) But yes, I agree that if Shinichi had to choose between cease being a detective or losing Ran, he would most definitely choose the girl.
I would explain, myself, all of the instances where Shinichi showed interest in science, but I'll just leave that to Kyuu.