If the copyright assignment was to FSF, then someone having a fencepost account can confirm if you are on the list. I cannot.
Based on some recent discussions, the bug report email is meant for everything: bug reports, feature requests, patch submissions, etc
No. Those end up on the bug-gnu-emacs mailing list. I believe almost all core developers subscribe to that. Normally, when I submit a patch, I CC one or two people whose code I am modifying. (The new vc-region-history command in emacs 25.1 is really useful for that.) If you do not get a feedback in about a week or so, it might be useful copying emacs-devel mailing list and referring them to the bug thread to see if anyone can review and commit it for you.
Yeah, the patch submitter needs to ping emacs-devel if they don't get any response to their update.
I have always sent patches via Google Inbox. They ended up fine. The only instance where I had to send a patch as an attachment was when it contained both tab and space characters (I was trying to not mess up the original whitespace). In such cases, you need to send the patch as an attachment. Nowadays, with recent commits you will rarely find the tab chars in the patch diffs (which is a good thing!). So inline patches work just fine.
For reading sanity, I always send emails via Gmail/Inbox without any rich text formatting.