as far as I know the scheduled scan is initiated by the agent invoking VirusScan locally. So if the computer is sleeping, the agent sleeps as well & nothing gets the agent wake up and initiate the scan this way. ePO will not reach down and pull the computer out of it sleep. Most likely.
(On second thought: you might schedule a server task with e.g. Search Systems as primary action and then performing a wakeup call on the result (sub action) that does try to wake up the agents by trying to contact them, if that's enough for waking up the computer, then chances are the agent wakes up too and runs the task. However, putting computer back to sleep could be dubious and you need to synchronize this task to the scan schedules)
Your second option seems ok, the Schedule option of a client task contains option to run the task when computer has been inactive for X minutes.
You can inititate scans of several type (scope) and one or more in a day or a week. Run a full scan every two weeks or once in a month and run a scan with limited scan scope every two days or similarly. You'll have quite a few scans defined but that's ok.
Thanks for your reply.