Electrical panel clearance may be an issue. Think you need like 30" width clearance which can be off-center to push it up to the panel edge. Looks tight from the picture.

Add some fire blocking on the wall penetrations if that is going to an interior wall from a garage.

Is your pex rated to handle the pressure relief valve temperatures and is the inner diameter equal to or larger than the valve opening?

Is there an air gap on your pressure relief drain? (can’t see where it terminates.

Might need an expansion tank is needed.

As others said: drain pan, straps

Had a nicer formatting post writen but lost it when trying to post during site outage.