Again, if you review the tutorials linked above, as well and view others on the blog, you’ll find that all of the problems you just mentioned are already solved.
You can view an existing entry, you can edit the entry, and you can submit native Webflow forms without the success/error message replacing the form (or use other services mentioned to keep the form entirely without it being dismissed).
…and you can do all of this while getting the data off the page without writing a bunch of bespoke, custom Javascript.
It’s all there for you 
Good luck!