Every entry grants you 180 days max stay, with 1 opportunity to extend that stay. By a further 180 days. Then you have to leave and can repeat the above.

Yes when extending a stay you will need docs and likely have to show savings, as already confirmed. So it's easier to just leave and fly straight back in to get a new 180 days.

If you have a dog then make sure you have a back up plan incase anything happens reentering