i will answer your questions after i make a couple of brief comments and the answers to the questions i will give will focus upon what parts are most important for you right now.
first off let me say that i would not worry about snap very much at this stage in your game. from my experiences and my experiences teaching others, it can make your game a mess from anywhere from 1 to 12 weeks but yields benefit in the long run.
secondly, the conceptual aspect of snap and the timing necessary to actually increase it are probably not appropriate for you to be considering at this point in time of your game. in fact, i only recommend it for people who have found themself at that overly common plateau in the mid-300's and are willing to throw their game off for a while. some people are lucky and are able to bypass this plateau and throw 400+ without having to think about it. most people are not these people.
as for stuff you need to know, the article that got me throwing 340' after 2 months of playing disc golf is: http://www.discgolfreview.com/resources ... form.shtml
as for your questions on slinging vs. snap. i'm really not sure what you mean by slinging, but i am going to assume that you mean, actually letting go of the disc after you have gotten it up to speed. the key is that on drives, the disc must rip out of your hand. on approaches and finesse shots, you may use more of a slide grip, but for drives, you need to have a firm grip where the force of the disc trying to escape is greater than the strength of your fingers holding it in. the snap, or tendon bounce is simply a quick, unconscious motion of the wrist quickly coiling and uncoiling immediately before the disc rip.
if you think of a pitcher, they use an opposite bounce, where their wrist bends backwards and then bounces forwards right before the delivery. this is what separates the 85 MPH pitchers from the 98 MPH pitchers. arm speed can only take you so far, taking advantage of tendon stiffness is what pushes you over the top. however, in disc golf, you should be able to reach the 325-375' range without needing a lot of snap.
as for your grip questions, first, i will send you to:
http://hem.bredband.net/area46/engelska ... tkast.html
these should cover basic grip forms and the swedish site has pictures displaying correct wrist orientation (which will help in both nose angles and maximizing snap). you should also try to make sure you have the disc resting in the seam (lifeline) of your hand starting at the base of the palm and extending to the spot between the middle and index fingers.
your description of the power grip sounds fine. however, the focus should be pressing the disc into the seam of the hand and base of the thumb (meaty part of the palm that moves when you move your thumb).
for now, i recommend not focusing upon trying to time the grip and it's probably easiest for you to "dial in" your grip strength before you even start your throw. while max D throws are going to take a lot of grip strength at the right times, for now, i will say to grip tight enough to where the disc does not wobble around in your hand and you can keep it oriented on the plane you want. once you get a feel for the disc rip, you can probably start experimenting more with grip strength, and pressure points, etc. for now, it appears you are letting the disc slide out or trying to release it, which i can say right now will rob you of a ton of power as well as not generate a lot of spin on the disc. with sufficient speed and force on the disc, it should eject on its own. this will probably take a bit of adjustment.
as for what to focus on when throwing, here is the focal points i will give for now (that i can add to later):
1) firm grip in the wrist down position (see swedish site for picture of "wrist down")
2) make sure you get good upper body rotation.
3) let everything happen in the order it should happen in. that is, focus on having clean and smooth footwork and let the natural progression of feet to hips to torso to shoulders to arm to disc happen. the legs are what really generate the power. think "quick and smooth" more than "strong and powerful."
4) keep the disc close to your body during the pull through.
other things will come into play as you get comfortable such as follow through, grip strength, snap, etc. but i don't think you should worry about it now. most of the snap related topics will only work if you have the timing down to perform the basic motion well and that doesn't really happen until you are throwing 325+ consistently and accurately.
let me know if you have any more questions.