[color=magenta]No, unfortunately in the new GameBoy Advance games (Ruby, Sapphire, Emerald, FireRed, and LeafGreen) you can't trade to the older GameBoy games. (Red, Blue, Yellow, Gold, Silver, and Crystal.)
As for Wireless Trading, Ruby and Sapphire can't make use of the Wireless trading, you will have to use a link Cable to trade with those games. Wireless Adapter is only compatible with FireRed, LeafGreen, and Emerald.
Many Pokémon have been improved upon from the older games, especially with the addition of natures and abilities. Your starter Pokémon will be very useful throughout the game. All 3 are pretty good, Mudkip is my favorite, when it evolves it will also become part Ground-type, which cancels it's Electric weakness. (Although it gives it a double weakness to Grass, which is it's only weakness) In-game, you can get away with using most any kind of Pokémon. You will need to worry about serious training once you get access to the battle frontier, as it is the most challenging event ever in a Pokémon game. For now, just concentrate on using your favorite Pokémon.
You will also want to catch a Zigzagoon early on in the game. It isn't an especially good fighter, but it has the pickup ability, which means that every time you win a battle, either with a wild Pokémon or another trainer, it has a 10% chance of getting an item. You have to make sure that your Zigzagoon isn't holding an item though, or else it can't Pickup anything after a battle. In Emerald, the quality of the items that Zigzagoon and other Pokémon with the Pickup ability can obtain will increase every 10 levels, starting at Level 11, and every ten levels afterwards. Zigzagoon is also nice, because it, and it's evolution, Linoone, can learn many HM moves, which will help you get through the game.
Feel free to browse around the different threads and ask more questions about the games!!