On your route in Non Bua ...
Wat Tham Erawan is a must. Steps up to massive cave. Walk through cave (easy), up steps at back of cave to amazing view.
On leaving Udon...
Red Lotus Lake Kumphawapi
ทะเลบัวแดง กุมภวาปี
Get up early to be there by 9am latest. Then continue travel on to Sakon Nakhon.
Slight detour off Udon to Sakon Nakhon road, but Wat Phu Tok in Bueng Kan province is well worth it.
Don't believe the numpties saying there's nothing in Isaan, simply not true, and as place to visit or live as a farlang, it's definitely improved. +30 years ago visiting the wife's village near Sakon Nakhon was a bit of a chore, but the past 10 years has seen big supermarkets open, coffe shops, more decent places to stay, so now I love going.
Enjoy your trip, looks a great route.