With regards to the UK monetary notes... Yes, they are different sizes (the bigger the note - the higher the value). Yes, they are different colours. For the visually impaired - the UK polymer banknotes "do NOT feature literal  Braille" or Unified English Braille (UEB), but they use a 'similar' system of raised tactile dots and different sizes to help blind and partially sighted people identify them. But it is a simple, easy, quick to learn system for ANYONE visiting the UK!

Pound coins replaced the pound note in the 80s and it was probably a response to inflation and vending machines. It's a lot easier to add another coin choice to a vending machine than to overhaul its payment system to understand notes. 2 pound coins came later more as a utility. There have been attempts to introduce a 5 pound coin over the years but with so many systems swapping over to contactless that's unlikely to ever happen.

As an example (why coins are handy)... I needed to buy a packet of spaghetti, so stopped at the supermarket. I ran in, picked up the pack and went to pay. The 500g of spaghetti cost  £0.28p (yes just .28p - about 37 cents). I was NOT going to pay with a card or split a note (US - bill). I just took out the coins and paid with them... I also use coins for parking meters etc. I like our British coins.

In uk you might go months without even useing cash because contactlesspay absolutely everywhere and then its transfers ,so you can go months without even touching a note or  coin !

Best thing about this is if you leave it in your pockets during washing it has 0 effect on it

Australia has coins too but we don’t keep them in our pockets, we come home and put the higher denominations in a jar and use them for minor things, like some milk or bread from the local store.  If we accumulate too many, we can deposit them in the bank or give them to our kids for lunch at school.

Australia invented polymer bank notes back in 1988. The security is so high, it takes several different machines to create each process involved.  70 counties have started using our polymer tech, but the US declined, as did the European Union.  China, Russia, Vietnam, UK and many more countries have polymer notes.

coins used to be the countries reserve of metals like copper and silver. at one point the bronze "copper" coins were worth more as scrap than coins so they switched to coated steel. ~£4 worth of coins was a kilo of bronze at £7.50 which was an infinite money glitch to the people who worked that out

I know that we have coins here in the UK, but it is a long time since I have seen on. Everything I buy is contactless.

Before we went decimal there were 240 pennies to a pound all of them were in general far larger and weighing more.

Coins last longer and are harder to forge than bank notes, both reasons are sighted for the change from paper money to the plastic money for higher denominations,  in that only the Bank of England, or their printers, have access to the plastic to make the notes. The same applies to Scotland

Paper money only came in because the metal was needed for the Great War. Here in the UK parking machines will take a card or app to pay

The cost of Visas doesseem expensive when you say it all in one go. However remember these costs are spread  over at least 5 years. £1000 a year is really cheap compared to the Usa medical insurance payments where you can easily pay $10,000 a year for medical cover.

GBP 1.00 = USD 1.33 is the approx exchange rate.
We eliminated the £1 note in the 1980s as they were getting dirty and ripped so much quicker, and the £1 coin is more indestructible.

With coins I have a small plastic tub in my kitchen where every time I get home with coins in my pocket, they go in the tub. I use it as emergency money with about £200 there atm. Greets from England.

GGL didn’t mention that there are actually 7 entirely different series of banknotes in circulation in the UK - the Bank of England notes which will be accepted anywhere, and 3 sets from Scottish banks (Bank of Scotland, Royal Bank of Scotland, and Clydesdale Bank) and 3 sets from Northern Irish banks (Bank of Ireland, Danske Bank, and Ulster Bank). In theory you can spend all those throughout the UK, but in practice it can be difficult to get people to accept Scottish and especially Northern Irish notes outside their own area, because of unfamiliarity (until I first went to Northern Ireland when I was 67, I had only ever physically seen a Northern Irish note twice in my life!). Technically outside the UK, the governments of the Isle of Man, Guernsey, and Jersey also issue their own notes and coins, which are the same size as their UK equivalents but not accepted in the UK.

You are more likely to £5, £10 and £20 notes than you are to see a £50 note.

London is more expensive you were correct, however chain brands of supermarkets have set prices nationwide and its lower. But if you was to pay rent, eat at restaurants etc in London then yeah very expensive

I've not used cash in a very long time.

Rarely use cash. Prefer contactless