Why? Is there anything wrong in current company, or is it just money? Please note that very very rarely you'll get everything at same workplace. If you are gaining the money, you'd be losing something - say work pleasure, or big title, or something else. Please make sure if you are ready to do the tread-off
Well, suddenly, red flag went up in my mind. Of course, it might be a very good company, but for an IT company, if there's not much information available on internet, then it is quite strange. You should be very careful about it - and if you choose to attend the interview, you can outright ask them this question - why don't I see much data about your company on the internet?
Nothing. As long as company is good, and your resume and skills are good, nobody really cares about CMM levels these days. Of course, level 5 is good - no doubt, but that doesn't mean that level 3 is bad or something. Just FYI, Google is not a CMMI level 5 company Do you think that someone will not hire ex-Google employee, just because of that?
Well, even if prospective employer don't know about your company, they will try to find out. Only things matter here are - that you don't fake anything (you have actual experience, and the company is legitimate etc.) and that you have the knowledge about those technologies
I hope this helps.