How are all the damage bonuses applied?

Solution 1:

The basic answer to this question lies here, at Diablo 3 Reaper of Souls Guide: Damage Formula Explained. In summary, certain types of multipliers are added together, and then all multipliers are multiplied together.

The basic rule is that everything is multiplied together. Most factors start at 100%, and have multipliers added on. For example, +40% physical damage results in a 1.4 multiplier, and +20% primary skill damage results in a 1.2 multiplier when using that skill. Note that some multipliers are added together before the final calculation. For example, elemental damage, native weapon damage, and skill damage modifiers are added together to a base 100%.

So, to give numbers to the pieces you've included: (90 * Weapon Damage) * 1.4 * (1 + 0.25 + 0.15). When you get a critical, which will occur, on average, according to your critical hit chance, then the 400% damage is multiplied in as 5 (base 100% + 400% additional). So, if your weapon's minimum damage is 100, your total minimum damage would be 17,640. On a critical, your minimum damage would be 88,200 for that hit.

Note that other factors are in play in terms of your "character sheet" damage, such as the speed factor (so, your character sheet damage is balanced to give an average damage per second value). Doing this allows you to compare slower and faster weapons fairly, because you'll see the actual raw output from each weapon in a comparable fashion.