Hustii

At the same price the mb511 RGB is better but taste is also important  

Oh and if you picked the mb600l because of the ODD, there is the Focus G, similar to the mb511 but with acrylic panel instead.

Yes if you don't mind a bit of noise, the airflow on the mb511 is really good (mesh, RGB, tempered glass). It will be better than the mb600l.

Alright.
I calculated that 497 Watt is what is needed for the PC.
550 Watt PSU is enough? if modular gold?

I would change the CPU cooler (Dark Rock 4), the SSD (MX500) and the 5700XT Pulse instead.

Well I don't know that CPU cooler so I don't know how it performs. The A400 is known to be bad and the 5700XT Pulse is just better (lots of benchmark). Otherwise everything else is good but indeed as @Sajiko mention, check if 400w is enough.

Sapphire is really good and XFX completely fucked up their 5700 series, so Sapphire all the way. Powercolor is also good  

Yes !
 
No.
 
Big no !

No it's because blower card are terribly cooled and XFX Thicc II is the worst 5700 GPU card you can get.
The Red Devil on the contrary is really good
 

It's a good card too but if you can pay a little more the Nitro+ is even better  (i saw 467.81€) or even https://www.mindfactory.de/product_info.php/8GB-Gigabyte-Radeon-RX-5700-XT-GAMING-OC-8G_1326179.html at 409€

No this one is pretty good, Gamer Nexus and Hardwared Unboxed (and others) made reviews on it  

Thanks for the input!