Lights are a lot of joy in portraiture, and can get you creative results not possible with just natural light plus reflectors. On the other hand, natural light portraits are equally beautiful, and can look, well, more natural. If you could, consider renting a 3-head set-up, for a key light, fill, and a hair/rim, and just have a go at seeing if it wows you or not in a day or two. Then you will know if you should buy them.