...you should be pretty fine with 8GB RAM but keeps the option open for upgrading.
Also make sure you get a good Power Supply. So often prebuilds scrimp in this department, providing one that is just barely adequate for the components installed. If you can do it yourself, or know somebody who can help you put it together, I would suggest a custom build over an “of the shelf” system. Most of the store-bought systems are designed for the average home user who watches DVDs, streamd video, surfs the net, keeps recipe files etc. and never intends to really “push” the system hard. Having a heftier power supply not only means that it will not be required to operate near it’s peak output through most of its life, but also gives you “overhead” for future upgrades.
Cases are another consideration. Make sure you get one with excellent cooling (more than just one or two small fans) as well as adequate “breathing room”. The GPU will create heat, lots of heat, so will the CPU. It is better to err on a little “overkill:” here as well for it will pay itself back in longer service life and less risk of both a software and/or hardware crash due to overheating.
Another benefit of a custom build is you can install only the software you know you will need. Many prebuilds come bundled with a tonne of useless “bloatware” that saps CPU and memory resources.
I would also invest in or download one or more of the free security utilities rather than just depend on the built in Windows basic firewall and security utilities. Tha last thing you want is your investment to be compromised by viruses and malware.