How to handle multiple versions of a paper (e.g. conference and journal version)
You can change your workflow slightly:


Write a paper with full proofs, polish it, and upload to arxiv.
Prepare the conference version (fairly late). You will use version 1 as your starting point, but you can edit it freely. You can remove proofs and refer to the arxiv version. You can polish the story, introduction, etc. You may spot typos in the arxiv version, but do not worry about those too much. There is no need to revise the arxiv version yet if the typos are minor.
Prepare the journal version. The key thing is that you will use version 2 as the starting point, not version 1. Of course you will now copy-and-paste the full proofs from version 1, but the rest of the text comes from the conference version. Therefore the main matter has already automatically gone through all the revisions that were related to the preparation of the conference submission(s), addressing conference reviews, preparing the camera-ready conference paper, etc.


Now you can simply revise your arxiv submission by replacing it with the journal version, whenever the journal version is ready.

If you follow this approach, there is never need to maintain parallel versions. You will never need to worry about updating version x when you fix typos in version y. People interested in your work can read the first arxiv version early, and your final arxiv version is as well polished as the journal version.

Note that you can start phase 3 as soon as you have prepared the final camera-ready version of the conference paper. When the conference version finally appears, you can already have a preliminary draft of the journal version written, and you can use it to revise your arxiv submission if it seems to be a good idea.