Need Help with CoS assigning

[hammjav]

First Back ground of my situation:

I had valid leave to remain in the UK until 6 January 2015 as a Tier 4 migrant. Prior to the expiry of my current permission, I submitted an application under the EEA regulations (as a holding application to buy some time as my prospective employer request Tier 2 CoS Increase) to the Home Office which is currently pending. However, the CoS allocation finally came through today and we want to apply Tier 2 as soon as possible.

Now I have following issue and I would highly appreciate if senior member can guide me.

1. While creating and assigning under the option "Tier and category" which option shall I choose.
2. My employer wants me to start work asap, so what should we put as start date and how does it effect the application.
3. How do I proceed with my application as UKVI already has the other application pending?
4. What route is more beneficial in term terms of normal postal, Priority service or premium application.

Thanks in advance!!!