Music Composers Unite!
It seems to me that the traditional symphony has been gone for well over a century. The trouble with composing a symphony is isn't writing it, but hearing it. Unless you are very well connected you can forget a live performance, if that was the case you probably wouldn't be posting here. The virtual symphony is certainly a possibility but you'll always wonder what it would sound like in real life, plus to do it well that takes audio production skills and capability that will take years to acquire. If you have good audio production skills then go for it, but my first question would be what do you want to accomplish or express? A good story about your inspiration may assist you in finding a performance (or two).
I'd be the first to agree that the modern orchestra is an incredible instrument. There are so many things that are possible with it that your first task might be to be sure you have a very thorough grounding in orchestration. How well do you know your strings, woodwinds, brass and percussion. How well do you know the orchestral repertoire?
It's not my intention to rain on anyone's parade, but orchestral performance opportunities are so dear that you want to be sure you've made every effort that your symphony will be your best possible effort. Anything less and you'll be kicking yourself. Your composing and orchestration skills need to be at their best just in case you find a real opportunity to have your piece heard. Good luck