..... Looks like lots of good stuff in the entire post ....
The rest of the thread took off on ancillary topics. But the main gist of how I thought your questioned pointed, was #2 and #12 : Namely, that a good technique to "opening doors", is to become civically involved in your local museums and historical societies.
Be a "fly on the wall" for a year or so. Get to know people . Attend their monthly or quarterly meetings . Pay to join up. Volunteer to sort papers & books, man a desk, etc... (ie.: docent duties).
You don't state your true intentions for a year or more. Till you've gotten to know various persons. Because you want to make sure there's no archaeological purist-types there.
Once you know everyone on a first name basis, and are given your badge (ID'ing you as "museum guide" or whatever), then presto, that works wonders as an ice-breaker, when chatting up people about the history of their site. You're "doing research" (you say as you casually flash your credentials). And then morph that into permission to detect.
I've gotten into some HAIR-RAISING sites, via these credentials. But it took years and years. And it's amazing how this opens up "white glove research files" in other museums, when you get to carry a "letter of introduction", from your museum curator, to get you into someone else's archives, that might otherwise be non-digitized white glove stuff.
yeah yeah, fox guarding the hen-house
And it's actually kind of fun anyhow, to be involved in leading tours, manning a desk, etc.... Get to meet some nice folk.