Pop-up flashes should be avoided is possible and of-course if the pop up flash is the last resource, then by all means use it but a designated flash is much much better.
The 24-105 f4 L is a beautiful lens and the price is quite nice also. the constant aperture of f4 is awesome not to mention better built, better glass and faster AF if I am not mistaken. I would definitely drop the lens you got there and get the 24-105 f4 and a flash if you can swing it. Also good glass retains value and can be used for many years to come if its well taken care of.
The package u listed will serve you quite well for some time so nothing to worry about there but consider getting a flash also.