No, you are not allowed to ground your club in the bunker unless you are taking the actual stroke. If you ground the club in a practice swing or prior to taking the stroke it is a two shot penalty.
In a bunker you cannot ground your club or its a penalty. So i would say when the player gets a firm stance and grip is truly when a player takes his stance
yes, you can ground the club before you tee off the only time you can not ground your club is if you are in a bunker or hazard.
When you 'ground' your club you have caused your golf club to come in contact with the ground or another substance such as water, sand or weeds. Generally speaking the subject of grounding a club centres around hazards where you are not permitted to touch the surface or the weeds that exist within an area marked as a hazard. If a player grounds their club in any of these examples they are penalized two strokes for doing so. If a player grounds their club on the putting surface and the ball moves - by gravity, wind or anything else - there is a penalty for this as well.
Yes, if a bunker is marked GUR you are entitled to a free drop. To do so, you remove your ball from the bunker, and from the nearest point of relief you are allowed one club length, you drop your ball and play. If there is water in the bunker and there is no GUR marked you are allowed a free drop in the bunker, no nearer the hole. If you cannot get relief from the water you can either play it or you can take a penalty drop out of the bunker.