THE MAC MINI IS VERY COMPACT
The Mini is 7.77" wide, by 7.77" deep, and 1.4" high making it a small and powerful computer. This makes the procedure difficult. This requires you to take out several parts and then pull the motherboard out of the aluminum case in order to upgrade the ram.
THE MAC MINI'S MEMORY IS UPGRADABLE, BUT IT'S STORAGE ISN'T.
If you are thinking about buying a mini then look at getting the most storage you can afford. Also since the Mac Mini has ThunderBolt 3 ports which will transfer information up to 40Gbs per second you can plug in external storage so that you don't have to pay Apple's storage pricing.
The maximum amount of memory depends on the year and model version. The 2018 Mac Mini has a maximum ram capacity of 64gb of memory.
THE MAC MINI IS A GREAT SYSTEM IF YOU WANT A INEXPENSIVE ENTRY COST.
This makes it a great choice for developers who need an in house system for software development. It is also a great choice for hobbyists who want to get started with a Mac so they can learn the in's and out's of of the Mac's hardware and software.