For both Photoshop & Lightroom to work smoothly, the higher the RAM, the better it is!
Your new config will run just fine - for your work - which is photography.
I think the new Mac Mini range has integrated Intel HD 4000 graphics with no optional discrete GPU. Is that known to be OK with Photoshop CS6?
While it will not deliver 'blazing fast' performance, it has tested OK with Photoshop CS6 MGE recently and it has faired decently well in some benchmark reports. Since the OP insisted Mac Mini, I think he can go for it. Also, since his work demands more 'Photo-specific' editing, I guess he should be good. Not much 3D I assume!
Here are some references:
http://www.pugetsystems.com/labs/articles/Adobe-Photoshop-CS6-GPU-Acceleration-161 - Look at benchmark reports (images) for Z77 chipset
http://helpx.adobe.com/photoshop/kb/photoshop-cs6-gpu-faq.html - HD4000 has been tested with CS6 by Adobe
And I haven't heard of a 'reported failure' per se yet.