My recently acquired macmini with standard 4 G RAM / 500 G HDD is used also for watching TV and recording stuff; just to play it safe and have a smooth system, I upgraded to 8 GB RAM (easy) and since the experience on PC systems with SSDs is great, it should also get a SSD for the system and a large HDD for data.
Wouldn't qualify myself as a "maker", but I have already a two-digit number of laptop repairs / tunings under my belt. Fooling around with the latest generation of Apple hardware, however, is entirely another league, and the reason why I looked at iFixit first.
The quality and attention to detail of the guide really blew me out of the water - the tried and true repair team (me and my wife) had no problems following the steps. I liked to follow the pages, being closer to the second computer with the instructions, she preferred the slides, so happy back-and-forth switching ensued.
We managed to replace the HDD with the new SSD / HDD combo in a little over an hour.
Look ahead when browsing the slides; it pays to know already what's next. Several slides of one step are a godsend; you can rapidly switch back and forth to see, for example, how the PSU is removed much better than just looking at a still.
You notice how excellent the guide is when you have to deviate from it; in our example, when the procedure was not just adding a second device, but switching out the old one for two new ones.
Make extra sure that you think about what you are doing, don't be shy of documenting something (if you have a Mac, an iPhone is not far away). In our case, everything from Apple had to be moved from the old to the new HDD. Easy, isn't it? But I should have taken a picture of the original HDD.
EDIT: And think twice about adding non-Apple HDDs. I just learneD that in Desktop-Macs, there is a special firmware which keeps the fans at 1000rpm, non-Apple HDDs (can be the same model / manufacturer) make them go to 4500rpm.
That would explain the now audible fan noises from the mini.
We found two screws (see image, from the first HDD?) remaining on the table after everything was put together. Since there are no adverse effects (the whole stuff is tight enough nothing can move inside), I put them aside, but a proper photo of the original HDD could have saved us from that embarassment.