What about something like this that allows for a lot of flowers? Then you could hang one of those flower balls from the center? I think that would look amazing.

http://www.wedding-candles.ca/specialty/Arches/ARFT-70-0533-wh_jpg.htm

I think the arch you chose is a bit much for an outside wedding, but it wouldn't look horrible. Remember those flower balls are going to be quite pricey........so I hope you have that planned in the budget.