It's a question I get asked a lot, what knife should I get? Well, it depends, which I suppose is why people ask the question! What I can absolutely say is that no knife set needs more than 5 knives at most. Any knife set with 8 or 9 knives in it is selling you some redundant knives. I personally use 2 knives almost exclusively with an occasional third, which is a bread knife.
My two main knives are a 225mm (9") chef's knife, and a 120mm (4.75") petty knife. I own a paring knife that is around 90mm (3.5"), but I almost never use it as I don't really do any cooking that requires a knife that small. Any peeling gets done with a handheld peeler.
So you should get a 225mm chef's and a 120mm petty then? Well, not necessarily. My wife is slightly intimidated by the larger knife for instance, and uses a 170mm santoku knife. Smaller, lighter, and because of the santoku shape, has a much less aggressive point to it. The best knife to use is the one you feel most comfortable with.
If someone were to ask me for a set that could do everything they were likely to need, there would be 5 knives in it. It doesn't include any really specialist knives like a fish filleting knife, or a heavy knife for cutting through bones, but for everyday cooking here are 5 knives that should be able to do everything.
1: Chef's knife. Or any variant thereof! Anything from a 170mm santoku to a 250mm Japanese style gyuto will fit this bill. This knife is the one you will use for doing most of your meal prep. Fine with both veggies and proteins.
2: Petty/Utility knife. This one can be a bit vague at times, but generally it's the knife between a chefs knife and a paring knife. Size can range between 120mm and 160mm depending on maker and personal preference. Mine is 120mm and is used either in spaces that it's difficult to get a larger knife into (cutting the centres out of bell peppers for instance), or just making sandwiches.
3: Bread knife. Shouldn't need much explanation! A crusty sourdough loaf will be best cut with a good, dedicated bread knife.
4: Slicing/Carving knife. Depending on the size of chefs knife you've picked, this one might feel a bit redundant. For slicing boneless proteins though there's not much better than a long, thin knife that will carve them easily. Usually a little shorter in terms of blade height than a chefs knife, and anywhere between 240mm and 330mm in length.
5: Paring knife. As I mentioned earlier, I have one of these, but don't find much use for it. My petty knife can do pretty much everything, but if you want a shorter knife that you can wield easily in tight spaces, this is the one. Anywhere between 70mm and 90mm.
When imagining your own custom knife I recommend looking at the knives you have and thinking about how they could be improved. Do you have a 150mm knife that you wish was just a little bit longer? Or taller? I'm always happy to advise on what might be the best knife for you.
Of course if you have a collecting bug, then what knives you need becomes irrelevant. I only need 1 chefs knife, but somehow I have 5...
However if you try and ignore that, when it comes to the knives that I have out in my kitchen at one time I do try and practise what I preach. Here is my knife rack, and yes, that is a free spot at the top for when I get time to make myself a nice slicing knife!