Apart from autocad
Besides the display and the ssd size which would be more appropriate for my applications? Which would run faster for longer really.
you can do that work on an ipad.....
This is autocad own reccomendations for a mac on autocad 2015.
AutoCAD for Mac 2015 System Requirements
Apple® Mac® OS® X v10.8 or later (Mountain Lion); OS X v10.9 or later (Mavericks); OS X v10.10 or later (Yosemite)
Apple Mac Pro® 4,1 or later (Mac Pro® 5,1 or later recommended); MacBook® Pro 5,1 or later (MacBook Pro 10,1 with Retina Display or later recommended); iMac® 8.1 or later (iMac 11.1 or later recommended); Mac Mini 3.1 or later (Mac Mini 4.1 or later recommended); MacBook Air® 2.1 or later; MacBook® 5.1 or later (MacBook 7.1 or later recommended)
64-bit Intel CPU (Intel Core Duo CPU, 2 GHz or faster, recommended)
3 GB of RAM (4 GB recommended)
2.7 GB free disk space for download and installation (4 GB recommended)
All graphics cards on supported hardware
1,280 x 800 display with true color (2880 x 1800 with Retina Display recommended)
Apple Safari 5.0 or later
All Mac OS X supported language operating systems
Apple® Mouse, Apple Magic Mouse, Magic Trackpad, MacBook® Pro trackpad, or Microsoft-compliant mouse.
Download and installation from DVD
Mac OS X-compliant printer
I would reccomend the 13 inch rMBP for that, but you may get away with the new macbook with retina display.
To be honest 256gb is just about the minimum without external or networked attached storage.