Alright, two thoughts here:

1.) It's not absolutely necessary, but without something to tune you're going to be stuck at the limits of the stock ECU.

2.) If you plan on getting one later, the earlier you get it, the more familiar and comfortable you can and will be with it when you have to really start tuning on it later.

The EMS is a very nice system now that the majority of the kinks are out, and just about anyone can look over your maps for you with the software installed.