Am I missing something?
Why not at least initially pursue both with an emphasis on getting the job (and securing it) 100% and you still have ~1.5 years left? And how bad do you actually want to become a professor? With poor odds with the number of tenure-track positions heavily declining, but adjunct positions increasing greatly? Are you content with adjunct salary hopping from university to university for a decade after spending years on your PhD?
Your history department is separate within the same university you are applying for the position, how will the position know you've applied to graduate PhD schools your second year?
How does a PhD in History give you marketable skills outside the university setting? At least with an MA and the type of soft-work you'll be doing at the university you can parlay skills into hopefully a decent private sector job should the university academic setting give out from under you.
Ask yourself, what's my backup in private sector that needs a PhD in History that would be more beneficial than MA plus management and 'soft' skills with real work experience?
There's far too many PhD's these days that are pumped out on a revolving door of adjunct work without much bright future for the academic gigs you see your professors have down the hall. I have 2 friends like this with PhD's working at a state university in subjects other than hard sciences. Hell, you might make more long term with a MA and work experience and the option to advance in education for free than you would after all the struggle during and after your PhD.
PhD in History is not exactly PhD in Molecular Genetics. The idea that everyone needs one these days really waters them down. Not to mention all the changes in the bubble of academia that will likely take place in future.
Think long and hard if that's what you really want... What does the PhD give you tangibly that makes it actually worth pursing? If you can't answer that soundly to yourself, you're much more likely to regret long-term than if you jumped into the job market.
1. I think I'm going to try to initially go after both, but as I said applying to schools is expensive. I'm looking at spending between $1000 - $2000 on the application process, which isn't chump change for me.
2. I understand the realities of the PhD job market, and I've considered the above. I'm honestly not entirely sure.
4-7. Obviously doesn't, etc.