Slashing is hedged now by splitting stake and nominating by at least two ledgers. We also see in Polkadot's network data that a stake of over 1,000 DOT ensures we get in the top 256 nominators of a validator. Therefore: 500,000 DOT / 3 Ledgers / 3 Validators ~ 55,555 DOT may be nominated per validator. Meaning for the first stage, maximum stake per ledger may be, and is limited at 100,000 DOT.
Average expected DOT delegation reward APR is 13.94% according to stakingrewards.com
as of May 17th, 2022. Our own research shows an average of 12.55% APR before fees for all the nominator's stakes over 1,000 DOTs. Around one third of all the staked DOTs are now having less APR than average.
According to our simulations Lido's on Polkadot APR is expected at 16.5% APR. The actual result may vary and will be optimized throughout the life of the protocol.
Staking rewards accrue automatically because stDOT is a rebase token so your wallet balance reflects exactly the amount of DOTs staked in the relay chain. Smart contracts will be updating reward balances every 24 hours, after each Polkadot era ends.
Lido protocol fee is 10% of net staker rewards. That means having 16.5% APR for Lido on Polkadot, your net profit is 16.5% APR − 10% fee = 14.85%.