Hi Will,
1. Re licensing practices. Yes, there are positions in which the attorney focuses primarily on licensing.
2. MS vs. PhD. Firms will care, but it's not exactly clear how much. I recently met a biotech attorney at an evening forum and I asked her how much PhDs matter. She says it helps, but she also works with people with only a bachelors. I guess once someone gives you a chance, it's all about whether you can get the work done. I believe the PhD will help, but I can't say whether it will help enough to justify the time and expense and effort to get the PhD.
3. Like higher degress (see 2. above), additional degrees will always help. The question is "how much?" and whether it's enough to justify the costs (time, money, effort) to get the additional degree. I can't say whether it will help that much.
4. Even patent practice is difficult to start inhouse rather than in private practice (firm/solo). I suspect licensing is even more difficult to start inhouse vs. in a firm.
Your ideal practice is relatively common here in the Silicon Valley. It's been a while since I loitered around Palo Alto Square, but Cooley Godward used to have a reputation for focusing on biotech and for having an emphasis in licensing moreso than prosecution. As a licensing attorney in the Silicon Valley, you meet many principals in startups and many VCs. As you build these relationships over the years, you learn of various opportunities in various roles in startups and VC groups.
So, in short, the type of practice you want exists, and I can say for certain that it exists here in the Silicon Valley. I understand there are other geographical regions of startup activity, but I can't say much about the legal culture in those places. Perhaps others here can say something about that.
Regards.