I will be advisable for you to apply for 2nd extension on or before April 5, 2015, therefore yes you can apply in feb 2015. However, you will not be eligible for 5years continuos stay by April 5, 2018 being the last date for ILR on Tier 1 General visas. I think you can change to other Tier 1 categor...

You can apply anytime before the expiration of your visa but I will advice that you apply 28days before the expiration of the visa.

Yes, it's pretty okay, you can go for your appointment as scheduled. Best of luck!

I will suggest you put an evidence of having an accomodation in place(e.g council tax, bills etc) though not a requirement but its safer!