The Maltby Pure Trac milled putter is a true blade putter and is as good of a Carbon Steel milled putter as you will find anywhere. Its exceptional. I would put it up against any high end boutique putter.
I too have KBS Wedge shafts on my wedge heads with unmatched shafts in my two sets of irons. One set of Paderson TS shafts and one set of DG 105 S300. I swap the wedges into what ever set I will play that day. You could certainly pair up with the Nippon wedge shaft family and have a matched set but if you are happy with the play you have no leave well enough alone.
I like a heavier wedge shaft and I like the feel of the KBS. Wedge play is so different from your full fairway shots and most companies sell specific shafts for wedges so the Nippons are probably going to play a little different from your Modus 3 shafts. If you are happy with your wedge game dont overthink the issue.