Unless you are shooting to make 100 million a year, any company I have heard of (thinking Google, Microsoft, Apple etc..) will not consider that a big enough market and you should be fine.
Agree with the VC thing, but assuming you are doing it outside of work it shouldn't be a huge problem, but check with a lawyer.
(Whether this would stand up in court is dubious, but do you also want to go up against a billion-dollar company's crack legal team in court?)
Also, I've heard the main issue isn't actually getting sued, it's that VCs or investors won't even touch you if there's the slightest hint that you might not own your code. If your side-project takes off it's nice to be able to enlist other peoples' help instead of miring yourself in legalities.