1) Major differences of bitcoin core and bitcoin unlimited? Is it the configuration of size of block?
There are a lot of differences with these two not just only the configuration of the block size.
https://www.google.com.ph/amp/s/themerkle.com/bitcoin-core-vs-bitcoin-unlimited/amp/ 2) Since bitcoin is open source, which means if bitcoin unlimited want to change the consensus of blockchain like size of block, they can. Can they change the total supply of coins? Block retarget time and so?
They cant, no one can change the number of coins, but when they do the forking there will be 2 coins, splitting bitcoin into two.
3) Is satoshi nakamoto in bitcoin core team?
No, noone knows who he/them was or where them/he was, but the thing that he discovered bitcoin is the only proof that he existed.
4) Is this the first major hard fork bitcoin ever forked?
As far as I know, yes.
5) As both platform uses the bitcoin source code, even bitcoin unlimited allow block size cofiguration, bitcoin core is able to process all the "Unnatural way" of transaction?
I dont know.
6) Main purpose of btu hardfork?
Block size increment
Security
You can read it on the link.
