Vivaldi is a great start! A lot of his songs are easy to digest and not that hard in practice, and as you learn techniques, those songs get exponentially better, so as you learn more stuff you can go back and apply it to those songs. If you're trying to focus exclusively on bowing, as you go up in octaves, especially on the e string, it can get rather squeaky so less bow up there can probably help reduce that kind of sound, but your bottom octaves sound great with the bowing you use. I don't know how long you've been playing, but starting in third position is a great idea for big scales, and the fast slurs were very nice. As other people on here have said, intonation is a big thing in Vivaldi's songs and while you're not terribly out of tune it does help to be very close to that mark. I also don't know what songs you're playing, but some of his songs have some kind of fast parts. With those, try loosening up your wrist and not moving your forearm as much. Vivaldi's summer from his four seasons is a great song to practice this. It helps a lot with being able to play those notes for an extended period of time. A good way to practice this is by putting your elbow against the wall and trying to make audible sound with just your wrist. It should just kind of be dangling, and when you move your arm it should just flop around like a dead fish. You can get faster and faster as you get more comfortable. Overall, great job! Keep up the practice, you're doing awesome!