I agree with most of the comments here along the lines of first, there being no rules, and second do what feels comfortable and natural for YOU.

Again, it depends on what method of finger style you want to emulate. Different styles may require different approaches and technique.

I started out completely bare fingered, just using skin and no nails, and using thumb, index and middle with the pinky anchored. I tend to play a lot of stuff using alternating bass with the thumb, while the index and middle fill, and pick out melody notes...(ie: rags, Travis, Doc Watson, etc..) You get a very mellow, plush sort of sound with just skin, but I found that when I grew a bit of nail (as Bud describes in paragraph 1 of his post) it allowed me to get a little more aggressive in my attack and kind of ''dig into it'', and to a small extent altered the attack angle at which my fingers approach the strings...but I find with me there is a fine line between having just the right amount of skin/nail combination, and the nails getting just slightly too long where the strings can get caught in the groove of the nail....so it's something I'm on constant vigil for. When I use a thumbpick and bare fingers, the angle of attack is more elevated, and with the bare fingers compensating for the louder bass sound the overall sound is even more aggressive. The only nail I tend to keep a little longer is the one on the ring finger, when doing 4 fingered rolls and jazzier voicings. All in all, I would say that I prefer the sound of skin with a hint of nail for clarity of attack, and a thumbpick (ala Chet style)....BUT

...experiment, and find technique(s) that feel comfortable and controlable, and have fun exploring.