1. I bid on the project and in my opening message I write that I'd love to learn more about the project/client and am available for phone/Skype call. I'm finding more and more jobs that already request a quick Skype "interview" so that's fine by me. I've never been flagged (to my knowledge) by Upwork for providing my email or Skype name in Upwork messages.
2. 9 times out of 10 I end up redefining the project scope based on my conversation w/ the client. As an action item coming out of the call, I always tell the client I'll send them a 1-pager task summary with anticipated fees and timeline via email (which takes our communication off Upwork).
3. In that 1-pager, I have a standard payment section which includes non-Upwork services like paypal, venmo, etc. At this point it's about feeling the client out. I'm not actively trying to screw Upwork, but their new pricing is just ridiculous, so I'm also not too concerned about ethics here either. I've yet to have a client get offended at the thought of completing our transaction off Upwork's platform, but I also don't push the issue if I feel hesitation.
4. Also as part of my standard payment policy is 50% payment upfront with 50% upon completion. To this day I've only been left out to dry by a client once and it was only about $650. For projects with very large fees, I'll sometimes split the final 50% up into 25% at a certain mile marker and then 25% upon completion.
I should mention that I only work with growth/marketing/content jobs, typically strategy > execution. I also put a lot of stock into my ability to suss out job owners, though I'm fully aware that instincts can bite you in your ass.
I also try to get the client to put some "skin in the game" by way of connecting me to whatever software they use that is relevant to the project (GA, intercom, etc.). This goes a little way in creating mutual trust. (That said, the one client who screwed me over STILL has me as admin on a bunch of their services.)
Based on what you've posted, you are deliberately seeking out work on their service, and deliberately trying to close the deal off their service, to avoid giving them any cut, in knowing violation of their TOS.
It's one thing to say you don't mind screwing them over, because you don't like them. But it's disingenuous at best to pretend you're not actively screwing them over.