Before you go mad on holesaws, consider a step drill?

They are a round drill thus avoid the 3-sided hole of normal drills
and self-centre so if you centre-drill a hole to begin with they do a
very good job of ensuring the resulting hole is where you want it. The
downside is their depth is limited to about 4.5mm (it varies, just
look at the engineering drawing of the tool if available). Wonderful
tools for enclosures, glass reinforced polyester, ABS, polycarbonate
etc.