> How difficult would it be to get to a GS12, if I'm not on a ladder position?

If you've got a college degree and your 5-7 ladder is in the same field, you'd be on a great track.

I doubt you'd be able to jump straight from 7-12 since 12 requires a year of experience at the 11 level and it would be very hard to argue that your GS-7 job provided you with GS-11 equivalent experience, but I imagine you could probably get in on a 9-11 ladder pretty easily especially if your 5-7 job is competitive service.

From there you're just a good connection or desk audit away from 12.

Also, don't listen to the people saying you can't make it here on that salary, you absolutely can. As others have said you'll definitely need roommates, but thousands of people come here every year and find rooms in group houses. I know NPS Park Rangers start at GS-5 and there are a lot of them who work here and live together. I'm not sure how you'd connect with them (maybe there's a subreddit or message board somewhere?) but it might be a good place to look.