Give me choices

Ok so I have a lot of Champions's but I have 2995 rp. All my champions are: Camille Ashe Ahri Braum Karma Jax Jhin Jarvan IV Gnar Garen Katarina Karma Azir Allistar Aurelion Sol Kindred Master yi Nasus Nocturne Lucian Veigar Syndra Shaco Ryze Rammus Sejuani Tristana Vi Vel'koz Warwick Xayah Xin Zhao and Zac. Nocturne Master yi are m4 my main right now is Vel'koz (m2 soon to be m3). What do you guys think? Should I buy another champion or focus on the champions a lot. Sometimes I don't have a lot of time to play games because it's like 30 mins and over to finish, and I want vel'koz to be a mastery level 6. My other 2 main I like a lot are Katarina and Vi. You guys got any tips to getting vel'koz m6 in any game type that's less then 30 mins and what other champions should I buy? Should I buy hextech chests and keys or other champions? If so I'm really looking for champions who are easy to use and can deal damage in early mid and late game. If so you guys think of a champion I should buy please let me know and tell me a good explaintion on the champion I should by instead of saying "cause he's good and they are easy" tell me how they are easy to use and why they are good. Thank you!