Replacing a MAC Mini with new one...

Mesch,
Recommend getting the max amount of memory. If you later decide to try a different software package such as HQ Player, you will be glad to have as much memory as possible. Also, as file sizes and your library grow, loading art etc. will be faster with more memory. 

Not to derail your original thought process but have you also considered alternatives to the MacMini approach including keeping your library on a NAS in another room and going with a low powered streamer/renderer to play the music on the NAS (and online if interested too)? There are many products to consider and my experience using MacMini for years is leading me down that path. Computeraudiophile site has the detailed threads on most of the pros/cons to this approach and specific recommendations.
Have fun either way you decide, Cheers,
Spencer 

Mesch, that's same as my setup. I started using the macbook instead of the Mini to rip and download files that I store on the NAS. My plan is to sell the Mini when I receive my Sonore microRendu which will be available soon. Aside from concerns that the slide out drawer on the macbook is a little flimsy, no problems. As more of my new files arrive via download vs. disc rip, this will be even less of an issue.
The only real quirk I've had to deal with going to NAS from HDD connected to the Mini is that if I let my Macbook "go to sleep" overnight rather than shutting it down, sometimes Finder's ability to see the NAS gets lost overnight as I have the NAS automatically hibernating during the night. Rebooting the Mac in the a.m. fixes it. Cheers,
Spencer