Just to add, when I talk about f4, for me it's more a low light thing than shallow DOF 'issue'.
F4 is f4 for light gathering regardless of sensor size (though that one will be debated forever in some quarters) but equivalent to f6 in FF terms re. shallowness of DOF.
I'll take a faster aperture over a higher ISO if I can and this for me has always been the issue, the smaller the sensor, but anyway...
I'd be tempted to just go 18-55 and ONLY if it flags up any shortcomings, look beyond that.
Depends on your needs...
I have an f4 zoom for my FF camera and on anything other than a very bright day, it's not for me for indoor use.
2.8's are better/borderline and 1.8's and faster, night and day difference.
It also depends on your screen, EVF or LCD resolutions. Not that they directly affect image quality, but how you see things when shooting and f4 at a higher ISO on my S5 vs f1.8 at a much lower ISO on my S1H, again, night and day difference and as you age and your eyesight gets steadily worse, anything we can claw back is a good thing!