If you wanna be 100% on the safe side, install 10 risers, one for each evaporator.

It's up to you and based on what information your client gives you to determine what the smallest capacity will be that must be transported along the suction line.

If he runs in the weekend only one evaporator, then your smallest capacity will be that of this one evaporator.

You could also use the system we're using in supermarkets: open all the SV's at once 4 to 6 times a day so that you have max speed in the lines and oil returns easy.
Install then also a suction accumulator so that the returning oil doesn't harm the compressor.