Is it logical to work with one or is it safe to somehow use several? Can anyone help me out?
It is the best currency, and it is also the most secure, from various standpoints, although the algorithm is not quantum secure entirely, while some coins are quantum secure, but they dont have the mining power to give the additional security.
So it varies.
Every coin has its own promise, but I think copycats are worthless. At least if they dont add anything new to it, then BTC is already the de facto currency for that purpose.
So I tihnk BTC is the main reserve currency in the crypto world, while the other are for speculators mainly.