I was just using the pitch of the '328P TQFP pins as a spacing comparison to the spacing of the SSOP pins on your chips. Your pins are closer and trickier to solder by hand.
Did you see the youtube video that i posted before?I hope with that method could be easy to solder these pins. I choose the same package that there was in kickstarter project of original discussion. Is there a package more easy to solder but not bigger?
As I said, too small for me.
1) Make sure to leave clearance around the connectors JP1-JP4 for IDC headers
2) For my 1024 IOs is the idea to stack boards? It seems IC6 at least would prevent that.
The MCP23017 comes in an SO version, which is much easier to solder, but package is inevitably bigger.
The flat layout could interfere with the barrel jack and USB connector.The original connectors might interfere with the ICPS connector also.