On most (all?) types you start the right hand side engines first.
GPU connections are on the left hand side of the aircraft. On the EMB, and most other aircraft, if you need a ground start cart your APU is unserviceable.
This means you will also need a GPU to provide the electrics for the aircraft until one engine is running.
If you start engine #1 first, then the ground crew will have to disconnect the GPU which is in front of a running engine - not a good idea.
On the EMB190 the air connection is underneath the fuselage but on the EMB145, IIRC, the air start connector is on the left hand side of the fuselage, quite near engine#1.
On shutdown you normally shutdown left to right, so if your APU is not available you shut engine #1 off then connect GPU and shutdown engine #2.