problems configuring company-mode for auto completion key banding

[Krishnakant]

Dear all,
I had used Emacs about 10 years back .
After that there were severl things due to which I could not continue 
using it.
However now I wish to use it for my python programming.
I am a blind user and I use emacspeak with emacs for all my activities.
I have tryed configuring company-mode with Python.
Basically I use elpy-mode which intern uses company-mode.
The problem is that although default auto completion behavior  is 
perfectly good for sighted users, for me it is too much speech.
So what I was trying to do is to set company-mode not to auto complete 
automatically.
I was trying to set C-tab for auto competion.

But it still auto completes which I just type 3 chars.

Here is my init.el file:
(require 'package)
(add-to-list 'package-archives '("melpa" . "http://melpa.org/packages/";))
(add-to-list 'package-archives '("elpy" . 
"https://jorgenschaefer.github.io/packages/";))

(setq company-idle-delay nil)
;;(global-set-key [C-tab] (quote company-complete))
(global-set-key "C-tab" 'company-complete)
(global-set-key [f10] (quote python-mode))
;;(package-initialize)
;;(elpy-enable)



Note that I am very new to setting such things in Emacs.
So I have to manauly start python-mode when I open a .py file.  I am 
aware this is not correct but can't see what's wrong.
Would be happy if any one gives some tips or pointers or some example.
Happy hacking.
Krishnakant.