you probably want a powerklaw on the warboss. Its a powerfist that looks awesome. It is pretty much a necessity on any ork army list. Also get the warboss a bike and run him with the nobs on bikes.
Stormboyz are fun but for 500 points you kind of have to go one route or the other when it comes to fast attack. I would choose bikes any day. You get 5 toughness, and a cover save. And stormboyz have a chance to die when they use their jetpacks.
Without the stormboy, and with a bike and powerkalw on the warboss, you are pretty much set for 500 points
If you want to run the warboss with the boyz, get a bosspole, and get a powerklaw on a ork nob. (seriously those things are overpowered)
IDK about the proxy for warbikes. Some
GW stores are really tight about proxies, and they follow
WYSIWYG to their deaths, but some are like yeah whatever.
The army looks good. If you ask people at the store, they will pretty much tell you what I told you. Just some upgrades adjustments and you are all set to go.
In regards to gameplay, I would put your forces close enough so that they can help each other out, but far away enough so they split firepower. Good luck!