I will answer your questions one by one:
Releasing it on all platform (web based, iPhone, Android) and learning it yourself
Well, if you ask me, all this platforms are completely different from each other, I am a full time web developer and also have developed few native apps in Java for Android. Learning all this platforms may be possible for one person, but to expertise in all of them is not a one man show. There are alternatives like AIR, PhoneGap/HTML5, etc. But if you ask me, the performance and overall user experience that you get could not be compared with native development.
So, you can learn it yourself and can release it on all platforms, but 1) It will take time 2) You wont get professional quality, just like it was built by an expert 3) You would be able to develop small and simple apps, trust me Zynga Poker was not built by one person, the back-end infrastructure and servers etc. needs a lot of efforts and money.
Regarding getting professional help and sticking to your idea
Well, I also have several great app ideas that I am sure could make millions if implemented correctly, lot of us have them. But first we need to think, how your idea would change people's life or help them solve their problems, is there any need for it, or why would they use your app? There needs to be a lot of thinking before you can move ahead to investment.
Regarding getting professional help, I am sure it would cost you a lot if the implementation needs a lot of programming, that depends upon the idea you have and what needs to be done to implement it. Offering a share to programmers, would hardly work (based on my experience in industry). Getting an investor or making him agree on your idea that it would work is equally hard. But you can try your luck on kickstarter.com and angel.co
One more thing, like Michael Pryor said, not all app developer make a lot of money and there are many, many app developers who don't even get their investment back.
Hope this helps!