Driving from Greve to Venice

From Greve take the road through the Val di Greve (Greve River Valley) to Ferrone (lots of pine groves). Eventually you will end up on the via Cassia (SR2) toward Firenze. Get on the freeway (Raccordo Firenze-Siena till it ends. Then get on the toll freeway A1 direction Bologna. Follow directions to Bologna, then Padova, then Venezia. Stop at a rest stop (Area di Servizio) if you get hungry. There are restaurants of the Autogrill chain and of the Sarni chain at all rest stops.
Between Florence and Bologna you have two choices of freeways through the Apennines mountain range:
Variante di Valico: The new route 20 min faster almost all underground in tunnels
Panoramica: the old route. 20 min longer but you get to see some mountains.
North of Bologna it’s a flat plain that will bore you to death.

I was considering having lunch in Bologna and then heading east to Ravenna and driving up the coast. I was thinking this might be more scenic and we could stop along the way as we leisurly drive up.

If you want to visit Ravenna, you can do that.

However I hope you don't mind spending twice as long on the road. The Via Romea (SS309 or Strada Statale 309) from Ravenna to Venice (via Chioggia) is a two lane highway, often clogged with traffic (and trucks). Last time I drove to Venice coming from near Arezzo, I took it. Never again. I got frustrated by the traffic, trucks, and occasional road work. Once I got to Comacchio, headed West on the Raccordo freeway toward Ferrara and got on the A13 from there.

There is really nothing scenic about the Via Romea road. It's still on the same Po Valley flat plain and you won't be able to see the coast from it. It's a road in a swampy area similar to Florida. I would take that route only if you need to see Ravenna.