So far, from what I could read online (in this guide and on the wikia, among other sources):
Briefing screen
Pay grade
The pay grade for a mission indicates how much cash players can expect to get out of a mission -- source.
Also this thread suggests it can go up to 10 stars.
Day rate
The dayly income rate is a cash reward with a multiplier for the day a heist takes (e.g. 1x in The Bank Heists and 3x in the Rats Heist) -- source.
Contract pay
The contract payment is a flat amount of cash reward based on the number of white stars (pay grade) -- source.
Payday
The overall payday is the sum of the other two cash rewards (pay grade and contract pay) and will be shown on the map if you select a heist -- source.
Yellow bonuses
These bonuses come directly from the difficulty (or "risk") of the mission, pictured by the yellow skulls on this very same screen. Normal = no skull -- overkill = 3 skulls.
Debriefing screen
Instant cash and bag loot items
The instant cash it the one you loot and put in your pockets directly during the game (jewels, cash bundles, ...) The bags are those heavy packs of money, jewels or even drug you'll have to carry in order to achieve a mission.
Balance
This section contains the sum of all the amounts contained in the Income section ($332,400 in the example given in the question) distributed between two type of accounts: the offshore account and the spending cash.
Offshore account
The offshore account consist of most of the money players steal during the course of their heisting career.
The player has no way of interacting with their offshore account and is only used to show off how much the player has stolen -- source.
Since August 30 2013, you can use your offshore account to directly buy specific missions from Crime.net.
Spending cash
The cash you get, finally. In the given example, it's 10% of the total amount, but so far I couldn't find any precise calculation to know if that percentage can vary or not.
This is the offshore account money and 10% of that becomes you spendable cash. -- source.
All maps have different variation for each time you play it, and the difficulty will effect what appears in the map.
The things that change relating to the difficulty is things like ATM's, safe's, large safe, camera's, objectives, additional loot, etc.
For example on Four Store on difficulty normal - overkill there is normally atleast 1 ATM on the level, but in Deathwish the possibility of getting an ATM is extremely low if not impossible.
The same rule applies with security features. for example when playing the Ukrainian job on noraml - hard you will have normal safes where the tiara is store and when you go to play on overkil there will be Titan safes which cannot be blown up. and on Deathwish there will always be titan safes and potentially titan cameras which cannot be destroyed.
Best Answer
To earn each difficulty mask, you need to beat every heist on the respected difficulty to unlock the mask. This includes all DLCs as well.
(Source)
The Wiki also states for the difficulty mask:
It appears that two of the heists you do not have to do. The Steam Forum also says the Train Heist does not count either.
As a side note, I've experienced on console (prior to the free update) that these masks were locked even after beating every heist on every difficulty (I 100%ed the game and they were still locked). I'm not quite sure why they were still locked, perhaps the game was expecting the missions that the PC version of the game has and the console version does not to be beaten, making them impossible to obtain on console (pure speculation). But now that the free update is out, I haven't beaten all the new levels yet - nor do I own the DLC for some of the heist to test and see if they now unlock.