I need a magento extension creating to a specific spec.

General information for the website: This is a 1.9.2+ multi-site installation with 7-8 extensions
Description of requirements/features: We need a custom extension developing on our multi-site Magento platform that we can apply per website/store view. This will also need to save data per website/store view.

Mod work will include adding multi-select fields to the registration and account page and a separate multi select field to the magento checkout page. The values available in these multi-selects need to be fillable from the backend via a new menu which includes CSV import.

We then require development on our menu that will require the values entered in the new registration/account multi-select field to pre-fill some html links.

We also require some javascript to slightly change the multi select box functionality to as if you were always holding the control key.

Everything specified here must be contained in a magento extension that we can freely turn on/off in the magento admin panel.

I have a larger spec with illustrations available on request.
Specific technologies required: Magento Extensions
Extra notes: