AW2518H, adding second monitor?

I have the Dell Alienware AW2518H Nvidia G-Sync 240Hz monitor. I would like to add a second 25" monitor. What specifications do I need? Should the second monitor also be 240Hz and G-Sync?

I had an older 1440p 60Hz Dell monitor as secondary and the usual problems with stuttering/Hz while having a loading screen on screen 1 or watching Netflix on the secondary. What should I consider to avoid issues?