NO! NO! NO! That´s not a CPU for gaming!!! You don´t want this!!!
No… for a notebook is this resulution (mostly) okay, but not for desktop. Go for 1920x1080! Minimum 21,5". Difference is only 10-20€.
You must decide,… what is your limit (money)?! Sorry it´s useless to discuss about a 1200€ PC, and than buy one for 900€.
For a 900€ PC (with monitor, keybord, speekers) you don´t need 16GB Ram. Take 8GB and good. Upgrading memory is pretty easy. You can do it later.
The motherboard/cpu is the heard of the new system. You don´t upgrade this (or you have a complete new one)!
No, but the reputation looks okay.
German VAT 19%
Ireland VAT 23%