Google indexed so much in the list. Now I wanted to remove everything from my site.
Please remember, it is going to take some time for Google to remove, reindex, and update the indexed links for your site. So, patience is a major requirement as you for go this process.
If I have disallow all in robots.txt and send my sitemap.xml. Would google still be indexing my links?
The answer is no. Indexing will stop because you are disallowing all robots to index information further.
Should my sitemap cover the whole period of birth of my site? For example, I have this site which is 1 year old. Should I include the post from day 1 up today on the sitemap?
If the links are still there with pages which are actually on the site, keep those. If some of the pages are not there anymore, or has moved to a new URL, I would strongly suggest to update the sitemap to the current structure of your website.
Also, for my websites, I want all of my webpages to be indexed, so that would be the life of the site from day 1 when I created it.