HS or LS gears?

I’m making a drive that I want to gear up externally 5:3.
Do I need to use high strength gears?

I would suggest using high strength gears.
Last year I made 6 motor drivetrain geared together with 36T low strength gears.
Two of them snapped after about two hours of driving

I would highly recommend using HS gears.

Honestly I try to never use low-strength gears. Using HS gears on a drive certainly isn’t going to hurt it.