My idea is for a cloud-based web application aimed at undercutting/replacing current enterprise desktop applications which currently exist in my industry/profession which help with data analysis and decision making. More recently, licensing restrictions have hampered the sharing/distribution of the software to a point in which it is restrictive to use between multiple offices (the most commonly used software is locked to individual users on ONE computer), while at the same time licenses are prohibitively expensive in terms of cost. Bottom line, the software vendors have expensive products which have been slow to adapt to changing market conditions. Is it a fool's errand to take on an established industry? Is it possible to undercut the traditional enterprise software model with a highly portable (cloud-based), low cost product to drive? Will established competitors simply replicate my idea, rendering my development work moot? Do I research the web technologies more right now (I have some good ideas)? Do I write a business plan first and try to get advice on how to proceed from there? Help! Don't mind all my questions, I'm new to this. Thanks!
The two answers here are right in a sense to call to your attention what a challenging endeavour it will be, should you decide to pursue this, but neither actually answer your question as you've stated it.
You should begin developing this idea by doing customer development with other peers in your industry (outside your own organization) to see if they share your frustration with the current solution and share your enthusiasm for an idea of how it could be made better. Since you're active in this industry already, it should give you a breadth of contacts to reach out to. I'd encourage you not to ask friends or people who you have a very close relationship with as they are more likely to tell you what you want to hear.
After you've validated that you're not the only one frustrated by the current solution, I'd look at building a prototype that is able to illustrate your vision in sufficient way to begin speaking with real potential customers. It *sounds* as if there may be some regulatory or practical IT issues that might threaten the simplicity of a prototype, but sufficient to say, this is the next step in the process.
If you've been able to demonstrate demand for your solution as illustrated in the prototype, then you're well on your way. Of course, there is a *lot* of complexity in just these two steps alone and I'd be happy to discuss this.
To answer the other parts of your question:
It's a waste of time to write a business plan. You can look at "Lean Canvass" as a means to inform your thesis and keep track of it's validation and evolution.
Established competitors will not move nearly as fast as you and can't "start from scratch." If you're very successful, they will copy you, but it's likely that it won't hurt your business too much if you get to the point where they are wanting to copy you.
I run a venture-backed enterprise software company and have helped many Clarity members through questions of this exact nature. I encourage you to read my reviews and book a call if you'd like to talk through these questions in more detail.