[wmf]

My first idea was flooding with almost non worthy transactions therefore wasting the miners. This was quickly debunked as I found out the miners would ignore 'empty' transactions.

Also, you have to pay a fee for each transaction and thus you'd have to pay (at least) thousands of dollars of fees to clog a blockchain. https://bravenewcoin.com/news/bitcoin-spam-attack-stressed-n...

Another idea is, what if I as user A say want to transfer to user B, but I mention an amount of coins that actually I do not own and spam it. Would the miners have to traverse all the way to the back or are there 'checkpoints' that can assure short travels?

The miners keep an index of how much money everyone has (unspent transaction output index) so they can immediately ignore such invalid transactions.

The last one is a bit more difficult. However can a big enough network of nodes, insert itself and start crunching the chain errors-fully on purpose to 'break' the chain?

This is similar to what people call the eclipse attack. However, if a victim node can connect to even one other node that gives it a copy of the correct blockchain then the victim will ignore the errors and use the correct chain. https://www.usenix.org/node/190891