I have a mac mini as well as a 27" Apple monitor and the aforesaid magic mouse.
So, I suspect your keyboard is running on Wifi rather than hard wired. If so, you might want to check your Wifi supplier… ours is a cable TV supplier, here in the U.S. and after several complaints, they replaced the wifi router with a newer model. Can't hurt to check.
Secondly, you'll find that the magic mouse occasionally just quits functioning and says on the screen… Here's the little secret that most have found greatly improves that problem. Remove the battery cover on the back and fold a piece of paper in two and the trim it with scissors to snugly fit on top of the batteries… replace the battery lid. No one seems to know why, but it does help with the disconnect problem.
I like the mouse and mac in general, but miss the ability inherent in windows to easily "cut and paste" by shading the item with the right key on the mouse held down and then right clicking "cut" or "copy", moving to the destination and clicking paste… oh know, not with mac. You still high-light the item with the right side of the mouse depressed, as with windows, but then, with the area highlighted, one depresses the command key (either side of the space bar on the keyboard) at the same time depressing the "c" key. Then when the destination is selected and the cursor placed where you want to paste it, again, hold the "command" key and at the same time press "v".
There's an endless litany of command-key match ups to achieve various tasks… but the casual user only needs to know a double handful…
Don't overlook the double tap function of the mouse as well as the "two-finger-swipe" to move the display right or left one page…
All in all, I'm happy with the selection after years of windows operating systems… Nice not to have to constantly download virus protection as with Windows… Best of luck. (BTW, Lotsa information on You Tube on how to do things)