I was in the same boat as you about five years ago. I naturally have a dark blonde/light brown color. I wanted a really light ash blonde color, like I had when I was younger. So after several coloring attempts with at home color kits, I gave up and went to a colorist. Basically she did what I asked, but was very hesitant about doing it. She got my hair so blonde, when I look back at pictures I am amazed now. However, I pretty much lost any curl I had. Granted, my curls are pretty loose to begin with. You know what it looks like when a curly tries to straighten their hair, and then walks out the door and it becomes this frizzy, wavy mess? Well, that was my hair ALL the time- and it never stopped breaking off.
I think it's important to note though that I had no idea how to properly take care of my hair. I was still using low quality store shampoo and conditioner, and I had no idea what a deep treatment or hair masque was. I attribute a lot of the damage to that. However, it has seriously scared the crap out of me of ever going lighter, even with just highlights. Just last November I finally cut the rest of the old blonde out- of course I'd dyed it back to my natural color, but that color had faded and that nasty damaged hair from the bleaching was still underneath it all.
I'd say that as long as you went to a good hairstylist you trust and properly care for your hair, things should be manageable. It may be gentler on your hair and easier to transition (not as much of a shock to your hair) if you tried getting highlights put in over a period of time.