1. Per the rules, you would not be able to deflect other attacks if you were huge than if you were medium. It might be a reasonable house rule to allow the deflection of boulders or ballista bolts for creatures of huge size, but then again I imagine it's the force of those attacks rather than their size that makes them difficult to deflect.
2. You could explain it as sliding between their legs, or running past them using the walls, parkour-style.
3. Yes, but remember that Shaping Focus only grants a benefit to multiclassed druids, and only up to your total character level. So you would need to have 4 non-druid levels in order to get maximum use out of the feat.
4. In my games, you would use your current DEX of 11 (and so not be able to effectively use Combat Reflexes). However, as this isn't one of the listed things a DEX-penalty adjusts, other GMs might let you use your original DEX of 15 for this purpose.
Well for the hallway thing keep in mind we're always talking five foot squares here. And since people are not usually five feet wide with dragon style it could easily be explained that you're simply lithe enough to skirt around your allies without hindering them or yourself.
You see now that could be a problem. But I Imagine it works the same way. You need a ten foot path to move as a large creature and even though you take up a ten foot space you are not actually ten feet wide. You double in size with every size you go up. so if you took up 3 feat of space, let's say at the shoulder, you technically only take up six feet of space as a large creature.
You could also flavor it like your allies pressing themselves up against the wall in an "Oh dear, here comes the gorilla" manner :)
As for the jumping tumble: You can use acrobatics to tumble during a jump, but they would be two separate acrobatics checks; bonuses to one wouldn't apply to the other.
It doesn't say it requires any kind of action. Just an attack and it can only be done once per round. So I don't see a mechanical problem. I have a character that just wears Gauntlets of giant fist. One of its abilities is it allows the wearer to make a free bull rush attempt every time it hits with an unarmed strike or natural attack. Often times creatures would give up and try a different method after getting shoved 20 feet back the second time.
That's what I was saying. I haven't seen anything about that either. And even if you only kick them back five feet they have to eat another attack just to get in range again.
I'm pretty sure as a large sized creature in a 5' hallway, regardless of the style feat you would be unable to charge. As a large size you would be using the squeezing rules which hinder movement and you cannot charge if your movement is hindered
Squeezing: In some cases, you may have to squeeze
into or through an area that isn’t as wide as the space you
take up. You can squeeze through or into a space that is at
least half as wide as your normal space. Each move into or
through a narrow space counts as if it were 2 squares, and
while squeezed in a narrow space, you take a –4 penalty on
attack rolls and a –4 penalty to AC.
When a Large creature (which normally takes up 4
squares) squeezes into a space that’s 1 square wide, the
creature’s miniature figure occupies 2 squares, centered
on the line between the 2 squares. For a bigger creature,
center the creature likewise in the area it squeezes into.
A creature can squeeze past a creature while moving but
it can’t end its movement in an occupied square.
bold = mine