what are the minimum requirements to run a full node? Can I use my normal pc to run a full node or do I need an extra pc? Does the fullnode have to be up 24/7? And where can I find the best description to set up a full node with only little knowledge in coding?
You can take a look at this https://medium.com/deviota/iota-nelson-ready-for-public-preview-a958c6d0a531
Its better when the PC is running 24/7 and you need a minimum of 4gb Ram and about 10gb free disk space.
Good luck! :-)
With regard to the last issue of your question you can find one of the best guide for setting up a full node on http://iota.partners/. The guide also says something about the minimum requirements for a full node (your main issue).
It is highly recommended that a full node works 24/7, otherwise it will frequently be out of synch and that could harm the Tangle for various reasons one of which is well explained in the third point of this answer.