The best angle airspeed is zero, or the windspeed, whichever results in a 90 degree climb, straight up. That's the best angle you can get, unless you consider a backward climb better.
This of course assumes enough available power for an OGE climb.
The only reason I know of for taking the throttle to full open is to insure that you know where the throttle is being set, and that there is no binding throughout the range. You want it under the idle stop before engaging the starter so you can take it to full off in the event of an electrical failure. If the battery gets too low during the start, and the temp starts going too high, you risk not having enough battery voltage to engage the idle stop solenoid, thus not being able to stop the fuel, resulting in a hot start. Below the stop, you can take the throttle to full off with no electrical power. But I've never heard of going to full throttle at 12% N1. You do that before initiating the start.