There are intellectual property concerns, there are trade marks, there is lawyer stuff.
These are things to consult an attorney for. Don't ask a bunch of programmers, ask someone who has both the legal training an experience to tell you what you need, when, and how to get it.
How do you begin to establish and protect your software/website/intellectual property, what are the cheap first steps, what steps can be postponed, and what must absolutely be completed before your software touches the public?
I am not an attorney and this is not legal advice, but it should help you figure out what questions you need to ask when you do talk to your attorney.
You're asking some questions here that you shouldn't concern yourself with. At the moment, all you need is your Trademarks. If you accept user-generated content, you'll want to also appoint an attorney as your DMCA agent (so that you can enjoy "Safe Harbor" protections in the US).
You do not need to be concerned with so-called "intellectual property" at this stage, not least because "IP" is a fallacious, non-existent concept. Copyright, Patent, and Trademark laws are not property rights, and you should not think of them as such. They are legal monopoly protections; no more, no less. Moreover, aside from your Trademarks, you have nothing to be concerned about.
You should be concerned primarily about making your business work.
But I have some other notes:
In the US, if you wish to make things easier for yourself in Court, it's recommended that you register your Copyrighted works at the Library of Congress. Your attorney can assist you in this. It is not strictly necessary to put a © at the bottom of every page, but it does serve as a reminder to those who view it that it is protected under Copyright. But having the © on the page has no bearing as to whether your work is protected under Copyright. It is merely a notice. (There are a lot of misconceptions and confusion about how to protect your Copyright. Read Copyright.gov's FAQ.)
In the second matter of Trademarks: Trademark law protects you from anyone using the name of your company or project in a way that may confuse your customers. It does nothing else. You will need Trademark protection regardless, and it is recommended to get one early, ideally before release. Your attorney can help you with that.
In the third matter of Patents: Your work probably already violates at least one patent. It doesn't matter what it is or what it does; there's already a patent on some part of it. If you have patents of your own, you may be able to use it as a defense if or when another patent holder decides to sue. Your attorney may recommend patenting some aspects of your project, but you will find this a difficult prospect at best (since software enjoys fewer favorable Patent protections since In re Bilski and since there is so much prior art and academic work that may already have covered anything you might plan to patent). I'd also like to point out that if you have read or if you search for patents, then if someone sues you for violation and wins, they will win treble damages for your "willful" infringement. It is best if you avoid reading patents altogether, and that you ask your attorney not to search on your behalf.
Lastly, I want to point out that "owning" a patent on something does not really protect you from anything. Software patents in particular are frequently overturned, limiting their usefulness in Court. Moreover, taking an aggressive litigious stand with patents is counterproductive, because it takes your attention and capital away from running your business. If you have or plan to get patents, the only sensible route is to hold them defensively. That way, you can focus on growing your business and keeping your customers happy, and if someone does sue you for patent violation, you might be able to get a licensing agreement without wasting millions of dollars in Court. That said, it is not a sure thing: There are a lot of non-practicing entities who will sue you, and all you can do is fight it and get it overturned. (Which, for most software patents, is comparatively easy to do compared to other types of patents. There is often abundant prior art that the USPTO never saw.)
In regard to the idea of "intellectual property theft": I'd like to point out that there is no such thing as "intellectual theft," and it's dangerous to go down that rabbit hole. Again, patent, copyright, and trademark laws are not property laws, and infringements of those monopoly rights is not theft. No one can take your rights from you except the government. When someone violates one of your monopoly rights, it is merely infringement and nothing more. Thinking about it as property and theft of property is intellectually dishonest and leads you down a path where you will be more concerned about your monopoly rights even as your business crumbles and disappears into bankruptcy. You should not concern yourself with those who infringe on your works. as long as you can deliver a superior product, you won't need to fear any loss, since, really, nothing has been lost.