Hey Lisa, Max,
first of all, thank you for the purchase!
Since the screen sizes of viewing devices may vary greatly nowadays, I would recommend using full background images that would not have to be stretched even on the large typical monitors – i.e. 2560×1140 pixels. I would also highly recommend to pay extra attention to how much disk space such images take up – in case any single picture is larger than 500 Kb, I’d suggest downsampling it (i.e. increasing the compression rate) – to reach a tradeoff between quality and size.
Should you have other questions about the theme, do not hesitate to ask!
Sincerely,
Andrii / Satori Studio