I'd personally go Green Escanor, Red Merlin, and Red Gowther as your main for a start. You can use Red Howzer as temporary sub to increase Green Escanor's stats. As you go further into the game you'll get better heroes for your PVP team. Just my 2 cents. Enjoy!
I personally would go for green escanor, red gowther, red arthur. For sub, use red howzer. Red arthur unique will increase escanor stats and he can give buff. Btw, I have an account to let go for free if you want since I didn’t play that account anymore. Got sariel,green gowther, green estarossa and many more.