If i select ETH and BTC as rebalancing pairs 50% of each
will trade ETH/BTC pair only and will calculate amount of USDT for BTC and ETH value or will trade it via USDT trading pairs BTC and ETH to rebalance it?
Yes, for now it is moving through USDT since not all token has direct way to trade. but keep in mind, the portion that being sold to be rebalanced is only a small portion, not the whole token holdings. You might see hundreds of transaction but the fees you paid is very small for each trades depend on how much portion it being traded.