Tier1 extension

[ohgod]

Hi ,
I am planning to apply (postal) for my extension next week. Currently holding HSMP (new) and extension to tier one
What are the documents I need to submit:
1. Application form (£820 by visa card).
2. 1 year bank statement.
3. 1 year salary slips (Formal one, but no stamp or company name. is it ok with letter from employer?)
4. Letter from office saying gross salary.
5. 2 photo in a sealed envelop.

Anything else?

English requirement, degree certificate or birth certificate?

I have few doubts regarding the application form:

B10. Home Office reference number(s) (if known):
Is this HSMP ref number?

D3. What date was the entry clearance or visa issued?
There is no issue date. Only valid from to valid to. Which one to put? No one clearly replied back in any previous forum topic.

Is cover letter is required?

Please Help.