Hey mate,
A few things I would say is make sure it has at least 4gb Ram to run your Djing software correctly and efficiently, mores great if you can get it but from what I know 4 does the job. As far as screen size is concerned I’d say the bigger the better really, I’ve got a 13inch macbook pro and it feels really small once Serato is loaded up, the resolution seems terrible as well even on the retina display model I have (that might be something I can change in the software though not sure I’ve just downloaded it).
I’m by no means an expert but I think something with a decent screen (15″ ish) and around 4GB RAM should be enough to be getting on with. The only other suggestion I’d give is try and keep it optimised for Djing, even if its just for tidiness. I use my Mac for college work, recording etc etc and finding everything I need when I need it can be a pain thankfully though with it being a Mac it doesn’t effect performance, I’d imagine lower end latops might start to struggle with too much software and memory taken up!
Hope this helps
Scott.