Cities of Sigmar Army Question

[jolly cargo]

Hey guys i'm kinda new to AOS (started a month before) and i already finished my SCE armies so i want to build Cities of Sigmar army next since i saw their upcoming infantry line and it looks cool.

But when i looked at Cities of Sigmar current minis in GW website first thing comes up in my mind is why Cities of Sigmar army consist of Warhammer Fantasy Minis??

Does the Cities of sigmar army lorewise limited to empire, dwarf, high/dark/wood elves minis? And is there any restriction on which empire unit i can add to army or i can use all of them and make it as freeguild unit??

For example i just bought these warhammer fantasy Free company militia units and can i add them as freeguild unit in my army?

[misty light]

You could use them as a proxy for handgunners
They consist of fantasy minis so people who have fantasy armies can play aos I guess

Quite a few armies are ports from fantasy

Or at least some of their models are

[jolly cargo]

Ah okay, and do i need to change square bases into round bases? I notice they all uses round bases while playing game