Help with Erica 22 by SennyK

Hi. My friend and I are trying to solve Erica 22 and it's a bit beyond our level. One of the commenters on Logic Masters said "first, standard gw procedures. then, one mid length chain to get the 7 in the middle. then one short chain to find the 3 in box 6. then a lot of basic sudoku" I was hoping someone more advanced than us could help us understand the chain that he's referring to. This is where we got on our own. I think/hope the chain starts somewhere around here?