to run smaller rears, you will need to get the lower pods. IRS or crc makes them.
for 19t a 96 will give you more room for larger pinions.
start with the batteries to the rear and if you need more steering flip the inserts and move the batts to the front
you want to mount the body as low as possible, so i woudl say the wire under the shock. but that would require that you remove the shock everytime you change batteries. but that is what i do