jazmin82, the promotion to SFO is automatic. Once you have 1500 hours TT and have completed a LPC you can apply to the CAA for a full ATPL. On receipt of this you are promoted to SFO. Depending on the timing of your sim check (LPC) will depend on exactly how many hours you have. As far as I remember you can claim up to 100hrs sim time so you can apply with 1400 hours. It will probably take between 18 to 24 months to get promoted.
At the moment it would be realistic to achieve a command within 7 years of starting. Maybe slightly less if market conditions are still good. After the 7 years you are transferred across to the DEP salary.
As I understand it you are allowed to leave at any point. There is nothing to force you to remain with Ezy for 7 years.
Hope this helps.