The rental car offices at VCE airport open from 8am to Midnight. So if your flight is delayed even slightly, you might be out of luck.
I don't know where you are flying from, but if you are coming from a transoceanic flight, you might also be jet lagged, so I don't know if getting in a car for a long drive is a good idea.
From VCE to Castelrotto, is mostly freeway driving, if you want the most direct and fast way. During the day, you might enjoy the drive through the mountains, however, since the views are fantastic.
How can the roads be well lit at night? Are mountains or country roads lit at night outside of built up areas in your country? For sure they aren't around here in California. They are pitch dark. You need to rely on your car headlights.
My suggestion is to stay in a hotel near the airport, and head to your destination in the morning. There is also a Courtyard by Marriott near the VCE airport, among several others:
http://www.marriott.com/hotels/travel/vcecy-courtyard-venice-airport/