The thought of extra release agent is good and bad. It's good because you'll be able to remove the action from the stock. It's bad because the thicker that coat, the worse the fit of the bare metal reciever to the stock. It's not much, but the goal is to make a perfect fit or as close to it as possible. On your first attempt, I'd lean towards too much rather than too little as it's easy enough to go back and do a very very light touch up coat but much harder to remove a glued in action.
Have an acetone or solvent ready and a TON of Q-Tips. If you did it right, the excess bedding will squeeze out a little. Q-tips with a little solvent will clean the the excess up well without making a mess of the stock.
Tape off all the areas of the stock you don't want bedding. It will squeeze out some so be prepared to clean it right after you tighten everything in while wet.
Look for any and all spots that overhang or excess could form into that would make removal tough, screw holes, pin holes, or even just an action that's a little too deep into the stock can all lead to the bedding arching past a neutral point and locking the action in place. Even if you don't think the bedding will get there, fill/plug any spots that possibly could cause issue. A few minutes first is worth a lot later.
When it's all done and dry, it's going to seem glued together. The action won't be free from the stock. It may take a bit of force too. I find a sharp palm whack on the end of the barrel often will "crack" the action free. It is often a loud pop that sounds like you broke it. But if you put a thin coat of release agent everywhere, it will come loose without an issue. The first time never feels comfortable though.
If the barrel channel on the stock is true, I like to wrap masking tape on the barrel to set my spacing. I'll wrap it more or less until the action sit's flush in the stock and the clearance is at least a business card thick. If you can't get the action to sit flush at that thickness, you need to remove wood from the barrel channel.
Also, don't be afraid to remove a little wood around the action screws. Having a bit thicker spot for the bedding compound to accumulate will lead to a stronger bedding. A skim coat, while looking good, has very little structural rigidity as the wood expands/compresses. Pillars are also a huge plus. At first I was overly worried that I bought the right size but if the are a little short bedding will fill in and make up for it.
The most important area is around the action screws. That's where the torque is applied and if that is solid, the rest falls into place. I'm not familiar with the 455 layout but if it only uses one action screw, I'd take a little extra wood out everywhere else and a little thicker coat of bedding. A single action screw can use all the help it can get. If it's multiple action screws, I'm really only interested in the area at the screws and middle area is mostly for appearance.
One final thought. Once you think you're ready, look it over again. Look over how everything fits, look over how everything is masked off, look over how the release agent is applied. That first time especially, it pays to measure twice and cut once.
