Varied questions (Size & Value)

I would like to get accurate answers about some banknotes and coins, I have tried to search online but the answers are always inconsistent:

1. What is the biggest coin and banknote in size currently in circulation?

2. What is the smallest coin and banknote in size currently in circulation?

3. What is the lowest coin and banknote in value currently in circulation?

4. What is the highest coin and banknote in value currently in circulation?

You'll need to define your questions more.  Biggest/smallest - weight/diameter/area (some square coins out there)?  Lowest/highest value - by exchange rate with US$ or some other currency or purchasing value in country of origin? Currently in circulation - common every day use or not demonetized?  

For instance, this is the smallest round coin in diameter that still can be used as legal tender:  N#6157  Would you count that?

You can do a search in Numista for some information such as this one for the largest circulating round coin by diameter still in use:

https://en.numista.com/catalogue/index.php?r=&ct=coin&im1=&im2=&tb=y&tc=y&cat=y&ru=&ca=3&no=&v=&i=&b=&d=&u=now&a=&dg=&m=&f=1&t=41-5000&w=&mt=&g=&se=&c=&wi=&sw=

I'm sorry I'm a new collector I didn't know that money is so different and come in every shape possible! 

What I mean by my questions to be more specific, round coins currently used on daily basis and what I mean by biggest and smallest is by diameter. Highest and lowest in value I mean in exchange by USD and also still in use on daily basis.

Good. You're welcome.  Welcome to Numista!

The reply has been updated, I would be thankful for your further guidance.

I'm afraid I won't be able to answer your questions.  You'll have to do some research yourself after you narrowed down the field with searches similar to what I showed above.  (I don't think it's possible to search by exchange value in Numista).  The search for largest coin I showed says this coin is the largest in diameter at 45.01mm: N#22258 I'm not from Tonga, I know no one from Tonga so I have no way of knowing if it is actually still used for everyday purchases.  That's where you'll have to do your own research.  If it's not then move on to the next biggest one and repeat.  There are no easy answers.

Thank you again sir!