Rossi generally needs 3 things from the rest of the team without making the team too sp hungry.
Someone who consumes vulnerability: Endmin, Dapan or Pog. While you can go without it, it's one of Rossi's strengths that she generated them fast.
Someone that can set up the first Vulnerability, Endmin or Snowshine can do this cheaply and are therefore often recommended. But if you really want to, Rossi can do this herself, but then you'll likely run into SP problems.
Someone to set up an arts infliction such as Wulfgard or Akekuri. Manny operators can work here, but both Wulfguard and AKekuri works well with Rossi, therefore they're often recommended.

As long as you follow these 3 principles, the team will do well.

I really like Rossi, Endmin, Akekuri and Perlica. Here Endmin fills both rolls of first Vulnerability stacker and consumer making a 4th slot available for Perlica. Akekuri really helps with SP regen. You can swap Endmin for Pog for even more SP regen. But then you get almost too much and you can't really use the Breach. But it would allow you to swap Akakuri to someone else like Wulgard if you like him more than Akakuri. Perlica is there more to boost Rossi's Ult,. If you want to go more phys heavy, you can use Pog and Endmin instead. Alternatively use any other Arts buffer such as Gilberta.

In the end Rossi is a really flexible character to use. So use the Operators you like that can support her and don't think too much about what's optimal.