Well, yes - ideally you want a Coach who can help you enter this sport safely and educatedly. This is a dangerous sport, that demands respect, regardless of what level you are doing. That's from GAG to 4*. Horses and Riders die doing this sport, and I've seen some nasty accidents at low levels.
So, when you venture into the sport, you want to be as prepared as you can be. Mentally and physically. Both horse and rider.
Do you have all the essential safety equipment? If not, do you have access to use of all essential safety equipement? Eventing Vest, Helmet, Medical Card?
At least you have someone to help you. You'll be doing 3 phases. Dressage, Cross Country and Stadium. Your friend should beable to help you out with preparing for these 3 phases and what to expect.
I highly encourage you to attend as many clinics as you can - even if you have to audit them - you will still learn a lot.
Welcome to the dark side! Stay safe!