H1 stamping London next week as contractor

Hi folks

I have interview for H1 next week at London embassy. Had few questions and would be great to get some help on these:

1) As contractor for 2.5 yrs in UK on tier 1, what documents do I need to show apart from usual ? I work through my own company as director and had contract with other UK based company. All genuine. My last day of contract is this week.

2) What is the approval rate in London embassy these days ?

3) Any specific questions for contractors ?

4) Sponsoring H1 through a "consultant", what should I keep in mind to NOT say ? My current and previous work has all been for big companies and hold a B.Tech deg.

Much appreciate any help.

G