I use 0.000001 BTC as fee. It takes a few hours to confirm, but I don't hurry
Generally speaking if you use this fee it will have the same effect as pushing a no fee transaction, so you might as well not include a fee.
The standard fee is 0.1 mBTC and its the same regardless of the amount of the transaction.
If the transaction size is big due to a lot of dust inputs then a higher transaction fee is necessary. All the transactions can be done with a 0 fee, but there is a chance that it may get and remain stuck.
It will not remain stuck if the miners do not confirm the transaction. If after 24 hours a tx is not confirmed then it will fall out of nodes' memory pool which will effectively make the inputs spendable again
I think the lowest transfer fee would be 0.0001 BTC, and the highest is up to you
the lowest fee is zero. The highest fee you will probably need is .0001 btc, however it may need to be higher if the transaction has a lot of inputs and/or outputs