Can I have a link to my extension page (in the web store) before I publish anything? I do not want to re-upload later for the sake of getting the link.
Your question is a bit unclear, but:
You upload an item to the Web Store as a draft before you get an option to publish. This does generate an ID that will persist between updates.
You can upload an publish an extension as "unlisted". Nobody will be able to find the extension without a direct link.
You can generate your future ID without using Chrome Web Store, if you package it yourself to generate a .pem file and later use this file to upload the extension to Web Store. More info here.
In either case, the final webstore link will then be https://chrome.google.com/webstore/detail/[yourExtensionIdHere]