Generally the airlines don't care much about your SEP hours, besides the point you have the minimum to apply for them. Generally most companies work with a factor calculations for such hours, and they amount for something like factor of 0.2 - 0.3 per PIC hour. So 100 hours PIC SEP, will count similar as 20 - 30 hours within the company for future upgrade etc.
There is no right answer, I know of instructors with 4000 - 5000 hours instructing, all their students got jobs before them. My CPL instructor, a great guy, had thousands of hours, and only got job 2 years after me with a Jet operator, despite having thousands of hours. But me and another FO that time, recommended him to management, and based on this he got an assessment, which he passed with flying colors.
What you will discover in this industry, it's much smaller than you might think, and it does help who you know, networking.