1: It seems to me transaction fees for "within 5 blocks" and "within 10 blocks" are very high. What do you think? Are these fees normal & usual these days when sending BTC's?
Those are probably right. Blocks are always full, which means that in most part of the time, you can't save money in fees and have a faster confirmation.
2: How long it will roughly take my BTC to arrive if I choose "within 25 blocks"? Do you think it is safe & reasonable to use it?
If you are not in a hurry to confirm your transaction, you can use the lower fee recommended or even edit your fee manually to a lower than the shown in the slider.
I have noticed that when number of sending addresses increase, fees also increase... This explains why fees so high for me.
This happens because fees are calculated in sat/byte. When you put more outputs/inputs, the transaction size increases, also increasing the fee.
