Well, It was a surprise for me to join a community and ask such questions as I've applied for many visas and never met such uncertainty on what I should do. Bravo VFS! Actually when living in Ukraine before we applied for UK visa twice and it was pretty straightforward. My problem is I always read and try to do exactly what's prescribed. With VFS handling the process you probably should be an artist...
So we applied from US as US residents but non-citizens.
Please help who knows the answers (who did this), I think that will help me and others too

Let's systemize this uncertainty:
1) UK government asked to provide full 10 years history of travel. Luckily we have older passports but that's still impossible. Some stamps are unreadable, some states do not stamp the passport (Israel) and we don't have all the records like e-mails, e-tickets etc. Technically we provided as much as possible but still missing some travels. Is it crucial? We remember ALL countries but they ask for specific exact dates and that's ridiculous.
2) Their website (UK Gov or VFS) somewhere (can't find where) tells that we should upload the passport and proof of residency in US. Or they propose to pay $75 so they scan for us. As we send passports anyway they still need a scan. Ok but what do they mean? First page with bio info and photo OR we should scan all pages or our passports? Can't find any details. What is the right answer?
3) They really demand scan of our passport and residency docs but on their website you see options to upload financial docs, employment docs and other typical types but no specific place to upload passport or residency docs. How should you upload passport? We decided to upload to "Other documents". So technically we did it, but... is this the right way to do this? Or we missed something. Their site is awful, buggy, unreliable and misguiding.
4) In their instructions they tell we should bring checklist and sign it during biometrics appointment but other people here tell USCIS ignores this document. What should we do with that checklist? Some recommendations are "upload to VFS" and we did that. But! Should we sign it before uploading? It should be signed both by applicant and by the officer. Should I attach my signature or just leave this field blank? Or just skip this doc?
5) In their instructions they tell this
Your biometric confirmation receipt will be stamped at your appointment. You then have 5 days to mail this, your application form, your passport and supporting documents to VFS Services USA Inc. All applications must be accompanied by a valid passport with at least one page blank on both sides. If the application is mailed without a passport the application will be refused.
What do they mean? That application form is what? We have some VFS document that includes some data and appointment info but it's not called Application. The only Application we have is actual Visa Application filled o UK Gov site. And they provided the way to download it but just for our records. This documet is more than 10 pages. Do they mean we should print our Visa Applications and send in paper form with passport? Or what Applications we should send with passports? Should we sign if printing?
6) The last nightmare is shipping labels. I spent several hours today trying to figure out. No shipping labels at their site, some broken link at UK Gov site... After reading this and other communities we understand they provided no info and everybody just visits UPS to order shipping labels. But what UPS service should we choose? And UPS askes to be specific with box size etc.VFS tells to include both shipping label and envelope so they return us documents. What size of envelope should we include? They also tell to send shipping label by e-mail if we forget to attach it. So envelope is not really necessary? You can't send envelope by e-mail.
Total confusion as we don't know what service to use, what size of the box or envelope (UPS operates boxes, never seen documents delivered by UPS actually, do they have envelopes of just boxes?), should we include envelope for return mail and what?
I feel like an idiot asking such questions so please excuse me. But I fear those guys just ruin our trip if we do something they consider "wrong". and their instructions are incomplete and conflicting. It seems like they do it purposefully to force people purchase expensive premium service.