Mods:
Thumb gusset also worked in rib.
To do this all created stitches between markers are worked in knit until enough stitches to for the rib pattern.
On second thumb gusset inc round, between markers,
m1, k1, p2, k1, m1.
Keep as established and working inc’s as knit for the 3rd, 4th, 5th inc rounds,
then work the 6th inc round as
m1,k1,p2, k2, p2, k2, p2, k1, m1.
Then continue as established and the thumb can be worked in rib.
I think this looks neater than suddenly starting the rib again on the thumb.

I picked up 2sts between each finger, making more finger sts otherwise I’d never have got them on comfortably.