The general configuration is as easy as it gets: a very straightforward install and then you just load Kontakt and drop the program in it. Then select the types of voices. You will probably take some time to get acquainted with the tool and develop a good workflow. You get to pick and choose consonants and wovels to build your words, which makes for a tiresome process. Actually some users developed utilities to solve this.
I've run Voices on an i5 with 6gb RAM, and it has never caused the slightest trouble. I use an M Audio Fastrack Pro card. The samples are not really that varied. There is for basic choirs, named Angels, Men, Woman, and Demons. Angels and Demons are just another set of Woman/Men choirs. Each one of these selections contains a number of preset sounds which you get to control via mod wheel. The samples are, in general, meant for a dramatic use (I do not see this software suiting mellow choral music). There are percussive effects and clusters.
I like the simplicity of Voices. I prefer to use it very sparingly, to create a particular effect in music. I did not try any other choral library before getting this one, but today I know for sure there is nothing in choral VST technology that approaches a realistic sound, even though VOXOS is fairly good and would probably be a better investment. Even knowing that, I prefer to stick with Voices because it suits my purposes. Voices is meant for a very specific use: create powerful choral backings and a bombastic sound.