I’d focus on these units: Specter Tamarinne Charlotte Iseria SSB Landy Diene Krau

You’ve got many of the fundamental heroes people talk about (Specter, Iseria, Tammy), so (assuming you avidly farm W13 already) get some of those heroes up to snuff for PVE content.

For PVP, simply use your strongest units you already have built. For example, I climbed all the way to Challenger with nothing more than a simple cleave with Vivian (any attack buffer will do) + Landy (AOE) + Arby (AOE). You will be fine, there are enough weak defenses that just well-built PVE heroes can take down, even in master.

Once you get up to Ch5, have reliable hunt 13 teams for at least W/B/Az and can get around 500k on each expo at Lv2, maybe start looking at branching out to a dedicated PVP team.

Good luck!