[1] If the price is increasing but the volume is decreasing. Why do we need to avoid such trades?
Because low volume could mean lack of interest which eventually could lead to decrease in price since when the volume is low enough even a little sell pressure can affect the price significantly, but as you probably already know it's not a 100% thing and there are always some exception.
[2] Regardless of how price is increasing or decreasing if the volume is low. Avoid such trades.
Again lack of interest is not a good sign and you should be really careful even if a coin/token keeps going up while the volume is considerably low.
[3] Regardless of how price is increasing or decreasing if the volume is high there is a good opportunity for trading.
It means that if the volume is up you can more safely trade that asset in the buy low-sell high sort of way and use that trading pair to trade on a daily basis without taking too much risk, these trading pairs are great specially for scalp traders.
[4] If a cryptoasset is experiencing sideways on a longer period of time and the volume is continuously increasing. Why is it that this is a sign of reversal?
Not sure this one is necessarily true, and if the asset is staying on sideways while has some increase in volume it can still just as easily keep going up in price.
[5] If there is an ongoing breakout and volume is too low. Avoid such trades?
Because that is possibly a trap by market makers to spend a little money to increase the price temporarily and make more people buy that asset so that they can sell at a higher price.
[6] If the price is continuously increasing while the volume is decreasing. Why is the this is another sign of trend reversal?
Refer to my answer to the first question.