I'd say probably Naughty or Adamant. Another way you can tell things like this is go to the pokemon's page and the Nature page of Bulbapedia. Check which stats are high and which are low, and choose a few natures that increase a low stat and decrease a high stat.
In Pokemon Omega Ruby, Latios can be found in Southern Island after obtaining the HM Surf and going to Route 123. To find Latias, you will need to get the Eon Ticket to fly to Southern Island to get her. Pokemon Alpha Sapphire has the same methods, but with the opposite Pokemon.
These Pokemon can be found before the National Dex: Latias (Alpha Sapphire), Latios (Omega Ruby), Kyogre (Alpha Sapphire), Groudon (Omega Ruby), Regirock, Regice, and Registeel. These Pokemon can only be obtained in the Delta Episode: Rayquaza and Deoxys. Post-National Dex Legendary Pokemon are: Regigigas, Ho-Oh (Omega Ruby), Lugia (Alpha Sapphire), Heatran, Mesprit, Uxie, Axelf, Palkia (Omega Ruby), Dialga (Alpha Sapphire), Giratina, Cobalion, Terrakion, Virizion, Reshiram (Omega Ruby), Zekrom (Alpha Sapphire), Kyurem, Raikou, Entei, Suicune, Tornadus (Omega Ruby), Thundurus (Alpha Sapphire), Landorus, and Cresselia.
There is no roller skate item in Alpha Sapphire.
You can catch Skitty in Pokemon Omega Ruby and Alpha Sapphire in the barks of trees.
You battle Kyogre for your chance to capture it in Pokemon Alpha Sapphire after you capture the groudon.
Magikarp
Yes, Tm's in Pokemon Omega Ruby and Alpha Sapphire are re-useable
No, you will need to trade for them or transfer them via Pokemon Bank to get them in Pokemon Omega Ruby and Alpha Sapphire.
Yes, you're given Latios after the Southern Island quest. Alpha Sapphire players get Latias, though you can get the other Lati in your version by acquiring an Eon Ticket.
Houndour can be obtained by trading from Pokemon X or Y. It cannot be caught in the wild in Pokemon Omega Ruby and Alpha Sapphire.
You will need to trade for Weedle or breed Kakuna. Kakuna can be found only in the Safari Zone in Pokemon Alpha Sapphire and Omega Ruby.
No