In theory, it’s possible w/ the current version of Ouroboros, as the selected stakeholders are already known at the beginning of the epochs. So, no one can stop you to shut down your PC and just turn it on and do a full resync (validating and downloading the missing blocks) before your turn (slot) to generate the block. However, the newer protocols will prevent this by obfuscating the list of selected stakeholders, means you will only know whether it’s your turn or not after the last generated block.
It just applies when you have enough stake to mint. So, it can only be properly calculated when the monetary incentives are known. Rough calculation is. If you have 1.4m ADA for stake, then you will be selected once in an epoch (5 days), means if the rewards for a month is smaller than your bills/costs then it not worth staking but delegating to a pool.
UPDATE: Just seen @vantuz-subhuman’s post, so pls check it for detailed answer.