Timpetou

Follow the advise of malcolmgin. During reassembly place the Mini on its front, and let the HDD or SSD (doesn't matter at all) slip into the two "rubber holes". This way everything is easier to see and to direct.

For me it was no prob to remove the fan just pulling carefully upwards.

Forget all the original plastic posts. I bought M3x20 (Sorry, I just know the measures of the "metric world" ;-)) plastic screws and according nuts in an ordinary DIY superstore. They fit perfectly. When fixing the heat sink it is recommended to get help from a second person. You should place the screws with springs from the upper side down through head sink and logic board with one hand while you simultaneously press on the heat sink on the processor. (Avoid canting it!) The helping person just tightens the nuts downside the logic board. Needless to explain that you should fix the screws diagonally.

As my experience you should definitely use angeled tweezers as shown in several pictures. To avoid stripped cable deflash sharp edges of the tweezers a little bit. I never experienced problems when using that kind of tool carefully.