How many romanceable characters is tough to say exactly - most characters will be romanceable in the future. It just may not make sense for the protag to develop a romantic relationship with them at this moment - for example, you might be able to date the freshman team coach in the future, but dating her now would throw a pretty major wrench in things right now plot-wise. So the player will be introduced to different romance options throughout the game at different times while other romanceable character paths will already be pretty far along. I'm hoping that approach allows for fresh gameplay throughout the life of the game, as you'll always have characters in different stages of your relationships to spend time with.
As for an estimate on length, hard to say. The first chapter will probably finish with v0.05, which is a ways away still. If I had to make a wild guess on how long the gameplay of the first chapter will end up being, I'd estimate between 10-15 hours? It's really hard to say since people read at different speeds, and some people want to avoid using hints and embrace the sandbox nature of the game, so it may take them longer to get through it.
Let's assume the contacts have the ability to regulate moisture in the eye and can keep the wearer's eyes healthy and happy so they can be worn 24/7 lol. I wear contacts IRL and I can't imagine a protag having to put them in every morning, or like...dropping them on the floor and having to clean them :o