You will always be able to transfer your contributions into your 401k.

You'll have to check with your employer's plan documents on how long it will take to becoming fully vested in the portion that your employer is contributing, there is no set number of years. Some dont' require vesting at all and the employer's contribution becomes yours immediately, others may have a vesting periods of a number of years. For example, if it takes 5 years to become fully vested, you'll be able to take 20% after the first year, 40% after the second year, 60% after the third year, etc.

Yes, if you leave the company you can do a rollover, and transfer your contributions to any financial institution such as Fideility, Vanguard or T. Rowe Price. Check with your company's HR department for information on how the employer's contributions are handled---at many companies you must work there for a certain number of years to receive part or all of the employer's contributions.