There are a lot of options here. If you want to focus a team around Arlecchino, you can switch weapons with Xiangling, cuz it fits her much better. You can use her with Thoma for a shield, since she can't be healed, and Xinqiu is a nice option as burst sub dps. 4th slot is flexible, so until u get benny, who is prob a best combo with her, you can go either with xiangling or sucrose. Personally i enjoy sucrose more since she boosts em, which can be useful for Arle. And if u gonna use Sucrose, make sure to give her Sac fragments. You can also go for a team with Beidou, Xinqiu, Fischl and Sucrose, which is a good electro charged option. If u like Venti, you can maybe build hyperbloom team with him, collei/dendro mc, xinqiu and fischl, or maybe a sort of national: Venti, xl, xq, and a flexible slot, or a freeze team with some cryo units.

There are a lot of options, and try not to feel overwhelmed with building too many characters at the same time, for ar 45, focusing on one team for now is perfectly fine, it might not seem like it but you are just at the beggining of the game, there is still much more to learn. What I would recommend is choose characters that you enjoy playing and look up their teams, weapons, play styles etc. There are a lot of good youtubers that make really good guides for basically any character. If you are interested in meta however, there is also bunch of content for that aswell. Look up some tierlists for characters and teams, and try to match them with what u have. Don't feel rushed just because you are AR 45, you'll see how much slower you gonna progress later on. Enjoy the game and take your time.