I recently put a small 400w system for my shed, mostly as a pilot project but also because I just wanted to do something different for lighting etc. Have room for 3kw on my house, but that's it. My property is too small and awkward for ground mount and not a lot of spots that get sun long enough. That one section of roof gets sun but rest get too many shadows. So I think the money that would go towards a 3kw system I'm better off saving to buy an off grid property as that is my ultimate dream. Then I'd have more room to build a proper ground mount system that is easier to access for maintenance and snow removal.
Still early to gauge and other than manually looking at the charge controller as I don't have any monitoring setup yet, but I figure I get around 50-60w out of the system on a good day. My panels face west so it's not optimal, and we don't get lot of sun here, so basically I'm relying on light from the sky in general and not direct sun. There was like 1 day with actual sun since the system has been installed.
As for going all DC, the issue with that is DC stuff is harder to find and more expensive. Breakers, switches, fuses, etc. Need thicker wiring for everything too. If you go DC straight to AC, then all the stuff you need for AC is easy to get at any hardware store, and the wiring can be smaller as the voltage is higher too. When I finish up wiring my system I will pretty much make it purely AC except the Raspberry Pi that monitors and controls everything will be DC. That way it can shut off the inverter but keep running.
One thing with a solar setup is snow removal too, that's extra work you need to be ready for. I've been going out mostly every day to clear the snow off. I need to build a platform to stand on so it can bring me high enough as right now I can barely reach it with the long pole broom. Something to consider if doing a whole house you need a way to get to them to take snow off.