Hey Alan,
I think you're asking a few things here.
First of all updating the database should be done in your processors. CRCs allow you to override any or all methods in the new class-based processors, and it's explained/showed here:
http://rtfm.modx.com/display/revolution20/Creating+a+Resource+Class+-+Step+4
There's not much in depth docs yet, but I'd advise to just open the resource update/create processor and see what it does, and what you would need to customize for your needs.
I think the second thing you're asking is how to change the fields in the Ext JS, which again really is just overriding methods. You'll need to register your own JS which takes the MODx.panel.Resource object, extends for example its getFields method and throws that into the page instead of the generic resource one. I've done some fiddling with this myself on a pet project, and while I do have it working this is not code that I am comfortable about sharing publicly (both to avoid people possibly mimicking my fooling around, and as this is to some extent bespoke work), but if you're really stuck and need some points do add me on skype or Google Talk and I'll see if I can help you out.
Back in Evo I did two sites with YAMS which really made sense (but was clunky / needed more work), and you really seem to be on the right track with something here.
Of course Shaun's Articles is a great example as well, though it does completely change things around which was (for me) confusing in the beginning.