If the whales are secretly buying up Bitcoin than I will buy Bitcoin at the current market rate. Even if it goes to 2500$. Gives me sum hope in the crypto space. Only if I find out they are buying through forums etc.
if this is such a good idea?

once the hysteria has broken out, the train has often already left. not only at the bitcoin but in general. rather invest regularly and smaller amounts to balance fluctuations as well as possible.
Actually, it could be a good strategy to monitor the largest wallets to see if they are accumulating, because reports are coming out that they were accumulating throughout the bear market and especially during the last stage of it. This could be seen as a leading indicator, with a lag of several months to a year to reflect into the price.