Stick with RPM a-arms. The aluminium just looks pretty and breaks easily, especially Integy.
What you have for your 4th question sounds good.
For your electronics you can run the Tekin RX8 system or the Castle Mamba Max Pro. Castle's newest Mamba is the Mamba Monster 2 which is waterproof (more water resistant) and can handle up to 6S lipo.
http://www.castlecreations.com/produ..._monster2.html
For battery power the higher the "S" the more power you are gonna get out of the battery and you are gonna go faster. I would start out with 2S or 3S batteries, they will keep your motor temps down and you will have more control. For a quality battery I would reccommend you try out SMC Batteries, alot of happy customers and they have great prices. A battery like this one would be great for you.
http://www.smc-racing.net/index.php?...product_id=123
Or this one for 3S
http://www.smc-racing.net/index.php?...product_id=138