Make sure you get the "Official Pi4 PSU". These are cheap and well engineered. Do not use a phone charger.
You should get an A1 class micro SD card
These Sandisk ones are popular:-
https://www.amazon.co.uk/SanDisk-microS ... way&sr=8-1
Assuming they are genuine, any of these cards will work including the 512GB one.
I use 128GB Sandisk A1 cards which are down to £20 now. 64Gb are £12.
The Official keyboard is fine, but it is compact. You may prefer a larger one.
You will need a micro-HDMI to HDMI cable - again, the official one is cheap and works properly.
I would avoid the official case - the Pi4 runs very hot in it and may throttle.
If you must have a case, then look at the FLIRC metal case (or the KODI version). The aluminium construction works as a natural heat sink. Make sure you get the Pi4 version of the case - you may have to wait a little as the Pi4 is very new.
In the mean time, the Pi4 of course runs very happily outside of a case.