Flexcut knives are just fine. They take a sharp edge, hold it well, and it's easy to bring them back with some stropping. My oldest Flexcut is about 20 years old, and it still works well. Helvies have fancier handles, but I am usually looking at the blade. I don't use them, so I can't say anything about their quality in hand. What I can say is that I have never been carving something and said to myself, "I wish I had the more expensive knife." I haven't hit the limit of what I can do with my Flexcuts, but maybe someone more experienced will weigh in too.
Blade shapes make a huge difference in the end result, particularly in the amount of finagling it takes to get there. Between the elongated handle and the bent teardrop handle I find the teardrop more comfortable; I don't like the palm tools, but I have long fingers and I may not have been using them right. You can do a lot with just a good chip-carving knife, but adding on a scorp, gouge, curved knife, and crooked knife will greatly expand your possibilities.
The other (possibly) big expense is your sharpening kit. You can go big commercial, waterstones, or get out a homemade strop, but it's something to think about before you start. Some woods will just murder your edge and having a fast, reliable way to get it back means actually finishing projects.