When I learned Vim, I started with the `vimtutor` tutorial. At the end of the tutorial, it suggests Learning the Vi Editor - by Linda Lamb (O’Reilly) for further reading. I found this book to be excellent for providing a solid grounding on Vi – and its descendants such as Vim. For a while, I constrained myself to using Vim in Vi-compatibilty mode before using the many wonderful features provided by Vim.
I try to keep my vimrc as lean as possible so that I’m not reliant on having it available (even though I have it in a Git repository on my VPS) and it’s only in the last couple of years that I’ve started adding plugins to it (Syntastic and Unicycle).
I've been using vim for years, but I completely disagree with your statement. I rarely find the "," key useful, so to me it was a no-brainer to switch to using it as the leader. I just have ",;" mapped to the functionality that "," used to do.
I use ";" all the time, but searching backwards just barely comes up. Usually, I'll hit "home" and then repeat my "f" search if I need it.
I use `,` as Leader, as well as to search back if I happen to `;` over something I was looking for. I don't mind waiting 400ms (my `timeoutlen`).