Lots of potential!
I'm a complete noob when it comes to classical and cinematic music but I've been a regular at the Audio Forum Lounge for so long now that I should be able to give you my 5 cents on this track.
At first I was surprised by the minor vibe you started with, considering your title suggests people are gonna listen to a happy track. The switch from a minor to a major progression around the middle came as another positive surprise, it was unexpected and it made me feel happy for some reason. I really liked that, it's not something you hear a lot so if you keep this up in more of your songs you could use it as a way of identifying yourself.
I really like the lead instrument too! What is it? Sounds like a mix between a classic guitar and a harpischord...
Downthings: like I said, I'm a stranger to cinematic but I keep hearing terms like 'East West', 'dynamics' and what not all the time. That said, I'm missing some reverb here. No, I'm missing A TON of reverb here. You're violin has some (I think?) but your snare is really tame. Adding some reverb (throw it on the master bus if needed) really adds depth to classical tracks.
Also the kicks. Need reverb, but it would be better if you'd replace the kicks with some timpani, that would contribute to the classical and epic feeling and would fit in better, in my opinion.
You've got a lot of work to do, but one can never stop improving! Listen to other tracks and what other people say, then you'll get the hang of things ;)
I actually made this song before i even knew about mixing! Haha. That's why there's little to no reverb, among other issues. Thank you so much though! c: