To be honest, I would go with it more or less as is. It has pretty much the right balance of enough kit to get you going, but easy access (via the software boutique) to other essential system items as you need them.
However, after installing 16.10 and then 17.04 and being less than impressed with their bugginess, I went back to UM 16.04.2. But, after installing it, found my web-cam no longer working and qbittorrent, my preferred torrent client, wouldn't run. As a consequence, I toyed with the idea, for a week or two, with going over to Manaro Mate.
I even went so far as to install it on bare metal and run it for a few days. I should say, that few days was a salutatary experience for me. No sound indicator - many popular themes, other than the pre-installed ones, would not run as advertised - all kinds of nonsense getting drives and partitions to auto-mount - several programs I use as standard not available - even in the AUR - much less busy community in terms of getting help....
There were quite a few other little niggles, but you get the picture.
For all the things I could winge about in UM (and I do winge), it is streets ahead of others in terms of being tidied up at the edges.
Finally, I am pleased to say, reinstalling UM 16.04.1 solved my webcam and qbittorrent problems.
So, all good...
As for an absolute minimal Ubuntu Mate environment, this can already be achieved via the server/mini install and then the installation of items as desired/required - including, of course, the Mate desktop. To be sure, it may take a few more steps to install a minimal Mate desktop than if it came out of the box. But, for people who want such a base and are knowledgeable enough and willing to build the rest themselves from scratch, these few extra steps are hardly onerous.