Oh a Mac guru! Thank you for responding :D
I was thinking to go for a 13" with 256GB and 8RAM.
As a designer, photoshop is getting more and more inconvenient and I almost replaced it completely with Figma. It's an online designer tool, but still in beta.
I think my pull factor is the amount of other designer tools and integrations available for Mac only. Sketch, craft etc.
Photoshop maybe easier now that it's subscription based but I'm not sure. I still use CS6 that I bought on disc years ago. Anyhow, I think you're going to be happier with a 15" screen. I have both and prefer the 15" when editing. Now with that said, the 13" is slightly easier for traveling...smaller and lighter.
You could probably get a more for your money buying PC but Mac does have some nice specific programs. I'm really digging Final Cut Pro X for example. Anyways, I would consider 16 GB RAM if all possible. The storage isn't too bad, you can always buy an external portable hard drive. I take a 2TB or 3TB portable HD when I take my 13" due to it's small storage.
Definitely planning on bringing a hard drive. Though, I do have plenty or storage in OneDrive.
Not sure about the screensize. Let's find out! I'll probably visit the store today and take a look.