Question: I want to define some key bindings for my new found usage of helm, amazing mode btw, and I want to do it without overwriting the usage of other keys. I realize that the number of different key combinations is infinite, but is there some way to see all *undefined* key bindings for say 1 level deep? 

For example, I want to know what key bindings are available after hitting `C-c`, and then get a buffer with a listing of `C-c some_keys`. 

Assuming this feature doesn't currently exist?

Answer: 
Here are few ideas. They don't answer your question directly but they can help you figure out which key bindings are available for use.

Get a list of all key bindings starting with a prefix
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The [`guide-key`](https://github.com/kai2nenobu/guide-key) package can be used to show, in alphabetical order, all the key bindings that begin with the entered prefix.

The below screen capture shows `guide-key` showing me all my key-bindings beginning with `C-x r`. As the available bindings are listed alphabetically, it's easy to figure out which bindings are available.

The screen capture also shows what other key prefixes I use `guide-key` for.

![My key bindings that begin with C-x r](https://i.stack.imgur.com/nDWbF.png)

Get a list of what bindings you overrode
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The `describe-personal-keybindings` function that comes with the [`use-package`](https://github.com/jwiegley/use-package) package shows what key bindings you overrode as shown in below screen capture. You can review the results of this function to check if you overrode a binding unintentionally. The cool thing is that this function shows the bindings for all minor modes too.

![Sample of what the output of describe-personal-keybindings looks like](https://i.stack.imgur.com/l5xiD.png)
[**Icicles** key completion](https://www.emacswiki.org/emacs/Icicles_-_Key_Completion) - `S-TAB` - shows you all key sequences currently available for use (i.e., bound, not free), including after you hit a prefix key. 

For example, `C-x r S-TAB` shows key sequences with the prefix `C-x r`.

Keys that are not listed are unbound (free).

You can sort the displayed key sequences in different ways, using `C-,`.