Hey Michael, no worries. Im not a fan of crowds either (its why I avoid the Taste of Chicago and other gazillion person events not to mention the traffic, et al).
Personally, when I go to this particular fest, I park west of Greektown, so I usually head west on Adams to about Aberdeen (last year I parked on freakin Racine) and hiked it.
http://maps.google.com/maps?q=adams+and+peoria,+chicago,+il&spn=0.011580,0.019855&hl=en. Youll end up parking on the street, but thats the way of it the neighborhood isnt too bad (some high end condos going up but its the city, but you know how that is. Alternatively, you can park east of 94 towards Wacker, etc.
But, seeing that youve got it made and are in the City (downtown) and to avoid parking woes with Marley (funny, my Pro5 is Mindy

), you can take the L (I think the blue line drops you right there off I-290 and Halsted/UIC stop its a short walk from the station: Downtown CTA map:
http://www.transitchicago.com/maps/maps/F2005D.html )from downtown or even hop a cab.
As for time of day, you can always go during the late afternoon/early evening (that way, you can maybe enjoy some coffee at Artopolis or even eat at a restaurant) and still have time afterwards to chill elsewhere. Its a madhouse after about 7 pm (its the last Greek fest really of the summer, so all the bad kids are still in town before heading off to school) until about may 11 pm when the shut it down and people all try to cram into the clubs/bars/restaurants, etc. A lot of it is S&M (stand and model), so be sure to dress appropriately you wouldnt want the Greeks of Chicago to criticize you two on first glance