Hello,
Please can you tell us the specification of the whole rig if you can and not only the cpu.
Which is you budget, how much you can spend?
Which resolution you would like to play, which resolution is your actual screen.
Which games you play?
To answer directly to your question, yes you should be able to install a GTX1030, i would maybe advice you to get a GTX1050 at least.
Regarding the AMD dual graphic, it work using both the AMD gpu inside the cpu and an AMD discrete gpu on the pci-express, in a crossfire fashion.
But dunno if the last AMD RX550/560 support this kind of dual graphic.
In any case either a GTX1030/RX550, GTX1050/RX560 are a good choice if you are on low budget but still want to play decently at 720p/1080p.
You can also check old second hand gpu like a RX270/370, RX280/RX380 or even a HD7970 are good candidates for decent 720p/1080p gaming.