Maria,
We drove that route last year - from southern Brittany to Blois via Tours.
On the Autoroute, just before Tours we were treated to an aerobatic display by a French Air Force Rafael (Eurofighter competitor) - just brilliant - right over the autoroute at low level.
Between Tours and Blois, the autoroute is quite boring, so the N152 on the north bank of the Loire is quite a change.
Just look out for traffic speed cameras on the N roads.
And in you are heading to the further side of Blois follow the signposted route that crosses the Loire and back again - the road otherwise continues through the main shopping area of Blois - which has parking on both sides of the road making it difficult enough without a van on the back.
Robert