"hoarding" is not the same as "saving". If you put money under your mattress, you are saving by hoarding. But if you deposit money in a savings account at a bank, you are saving, but you are not hoarding. This is a very important distinction. Hoarding removes the money from the economy, but investing does not.
Hoarding bitcoins is prevalent because there are very few ways to invest bitcoin savings. Investing bitcoins will be easy and common eventually and there will be no "hoarding problem".
Wrong, hoading is just a negative word for saving.
Putting the money in a bank is investing, at least in the current type of banks who invest or lend to businesses or private.
Saving is not a problem. A saved sum of money is taken out of the effective money supply for a while, but as the money has no value except its moneyness, it does not harm the economy, it only increases the value of the remaining money. This is normally innoticable, as some save and some use their savings according to their life situation.
It may become noticable if there is a major shift in the habit of savings, for example if people around the world at the same time believe that something bad is going to happen.
When you earn some money, or are given some money, you can
1) save
2) lend the money to someone for the market-decided interest rate.
3) invest in something safe for a return close to the market-decided interest rate
4) engage in some entrepreneural business with the opportunity for extra gain or risk of loss.
Most people want some money ready for needs in the immediate future. If you have too much for your liking, you would lend or invest. If you have too little cash, you could reduce your investments.