Sounds incredible. If you can really pull off double-blind at that scale it will be impressive, it's gonna take a gaming space with no less than 3 separate rooms, 4 would be ideal (Player A room, Player B room, GM room on which all units are visible on map, and Combat room in which mutually visible units are placed on the map and combat can be resolved with both teams present).
Most of us have some experience with games that large, considering we've had at least a couple like that in our Cincy group (the finale of the Clan campaign comes to mind). I really like the mix of mechs to armor/infantry you've got listed. That sounds more realistic in terms of what would actually hit a battlefield. Sure, there'd be as many mechs as possible, but for every mech you should see lots of conventional forces rolling up the beach alongside of them.
At this scale, with or without DB, it always seems that time can really get away from you during the movement phase. If movement will be simultaneous, have a loud kitchen timer ready, set for 5 minutes (or less), and anything that isn't moved by the end of it gets 6'ed. Look to use any possible shortcuts: visual spotting only, simultaneous movement, might even want to use the Battleforce/Quickstrike rules.
Good luck, I look forward to seeing the AAR.