What is your budget??
Start first with your case.
What is the make/model of your current dell pc?
Knowing that, we can determine if it is possible to reuse the case.
What dimensions are possible for your case?
The case you listed is a small ITX case with airflow that is probably no better than what you have now.
Then, the motherboard is a m-atx size which will not fit in the case.
The i3-8100 is not supported by the H110 based motherboard.
Nothing wrong with a sfx power supply, but 300w may be insufficient for a RX550 system:
http://www.realhardtechx.com/index_archivos/Page362.htm
and, it may not fit in a case that uses a ATX power supply.
I do not read your language, so I am unable to find a set of more appropriate products for you.