Nationals tourn over here, and my first time entering one, figured I'd like to make a good start. Rules can be found here, and I'd recommend checking them over, since some are quite... odd. Particularly the part about banned/restricted Pokemon.
The banned/restricted list is pretty logical. Banned = pokemon you can`t get except through special events (Mew and friends). Restricted = pokemon with 670+ base stats (except Slaking).
I`ve been thinking about this metagame a bit myself. Haven`t seen it mentioned yet, but from all I`ve read of others`analysis...expect enemy Mewtwo to run Explosion. (One person uses Explosion the other uses Protect is like...one of the standard 2v2 strategies). Also, the last two years rain dance teams were among the top of the metagame, and that`s when they didn`t have Kyogre. So...be prepared to beat rain dance teams, and expect a lot of rain dance hate (i.e. lots of people packing Thunder).
The moves to expect a lot of...moves that have been big before include Explosion, Earthquake, Surf, Fake Out; given the inclusion of ubers, I`d expect some Dragon. I`d expect a lot of Fake Out on the enemy Uber, and do something nasty with your Uber. As for which two Ubers will be good...Giratina-O is immune to Fake Out--that alone might make it worth using. Kyogre`s the most damage, but will probably get a lot of hate. Metwo`s the fastest. On speed, Palkia outspeeds most ubers, and can do horrible things to a lot of them--also has R4 to water, for people looking for more Kyogre hate. Rayquaza is similarly slightly faster than the default 90 with lots of damage--compared to Palkia remove the extra water resistance, but add that it nullifies rain (and Extremespeed is handy especially if you expect Fake Out).
Who`s left...Groudon is a weather-changer, which is always handy, but given the two-uber restriction it strikes me that the uber slot might be better used on a different weather changer--like one of the Hail people with priority ice moves to smash all those dragons (ObamaSnow and stuff). Lugia`s fast, but a wall--I`m not sure about walling as a strategy. Ho-Oh is weird--really not sure about running a fire type when water is expected to be common, but on paper Brave Bird, Sacred Fire, and Roost are ridiculous. Dialga...maybe--it`s not immune to Fake Out or Explosion like Giratina-O, but it resists them, loses some other relevant weaknesses (although goes from immune to weak against earth), isn`t locked into an item, and hits harder (less durability, mind). Regular Giratina...ultra tanky, but part of the appeal of Giratina-O is that it can`t be hit by Fake Out which means it gets to smash stuff, and regular Giratina does that less.
Hmm...one more thing to think about that just jumped to mind--the whole no sleep clause stuff and smeargle...Choice Scarf Smeargle (spamming Dark Void) sounds pretty plausible. This is 409 speed (faster than non-scarfed Mewtwo)...and 10 PP on Dark Void means this goes on for at least 5 turns. Not necessarily advising you use this (you`d likely win a couple rounds and then lose to the 80% hit rate hax--better to be consistent). Just...be ready to face it.
Oh yeah, something else to not lose to (this one`s always been a threat in 2v2, mind): Shedinja. You can hit it with Fire, Flying, Rock, Dark, and Ghost. You should probably have at least two pokemon with an attack of these types (given that ubers tends to see a lot of Steel and Psychic types, you probably were planning some Fire or Dark attacks anyway, but...).
Oh, one quick note--RNG abuse: last I checked it was tournament legal. I assume you already know this, but it`s worth mentioning before you spend hours breeding.
What else...oh, you asked about IVs; unless you have moral qualms about RNG abuse, max these out on anything you can breed. On ubers... The difference between best possible IVs and worst possible IVs is like...the difference between 84 base stat and 100 base stat. Average would be like...92 base stat instead of 100 base stat. Which is to say, even if your ubers have average IVs and your non-ubers have maxed IVs, the ubers are still worth using. The one I`d really watch is speed, especially on any uber you`re expecting to see mirrored.