1. Yes, I agree. More enemies mean a higher density of bullets, which makes the game more difficult. I think it would be better to tie the random number for enemy spawns to a timer. This would make it easy at the beginning and progressively harder over time, until the player is eventually overwhelmed by an unbearable number of enemies and dies. However, this preference also comes from the fact that I'm a fan of level-based games, so I lean towards having a clear final goal (even if it's a fated death), lol.
2. Using the 'R' key for reloading is perfectly fine, too. I don't feel there's a strong need to change it.
It's a very short and interesting game, and the opening animation was really fun. Nice work!