With respect to initial phase protection, people typically start with trade secret protection. You keep your idea secret and only tell people who sign an agreement promising to keep your secret -- those are called NDAs or CDAs: Non-Disclosure Agreements and Confidential Disclosure Agreement (those are synonyms).
During the pendency of your patent application, you can still be protected by trade secret until your patent application is published or your patent issues, whichever happens earlier. However, it's pretty hard to keep the secret while trying to market it.
In addition, there are reasons not to wait too long before filing your patent application.
As to what the odds are for ultimately getting a patent, they're pretty good assuming you're reasonably certain no one else has done the same thing before. However, the odds are appreciable that the value of what you get might not be worth the effort -- for example, you might only get a very narrow description of your patent right (a very narrow claim) that has little value in the marketplace. Some companies in the process of building a substantial portfolio won't mind if a few are narrow, but people for whom the value of each patent matters might decide not to spend much on a patent application of limited value.
The decision as to whether it's worthwhile to proceed with a particular application is strictly a business decision -- a weighing of the potential benefits of the patent (weighted by the probability of actually acquiring it) vs. the potential costs in getting the patent (in terms of time and money). No attorney can do that for you, unless they have specific experience in your particular business as a businessperson (not merely an attorney advising business people in your market). Valuation of property assets and evaluation of potential markets are strictly business things, not legal. However, what an attorney can do is help you assess the potential coverage, probability of success, and estimated cost to get the patent. Somebody else will have to supply the other parameters of the cost-benefit analysis.
I hope that helps.
Regards.