i think the best pair are BTC USDT ? is possible to trade only this or need difference the crypto ?
of course it is possible. you can earn 50usd or more if you trade daily with different types of coins . not all coins are down every single day because there are still coins that rising even if eth and btc is on a dip phase. another way to earn more than 50usd per day is to thru another business outside the crypto scene. non crypto businiess are verry stable beacause fiats are not volatile , in this way you can always earn a fix income as long as your business is indemand or in a targeted place for the public.