The question would require you speaking to an attorney to discuss the matter further in order for you to get any sort of guidance on this issue.

I agree with my colleague. For the interest of clarification, the answer to your initial question (would you need to seek permission from the original (copyright owner). I believe my colleague was answering "No," to your second question are there standard policies for sporting event pictures. No, there are no universal rules. Depending on the sources there may be sites that allow you to license the material or have guidelines for your use. You would need to consult those sites for their policies. But, the answer to your initial question would be "Yes." You would be advised to contact the copyright holder. Without spending too much time looking at the site you linked "History of the World Cup" (and no time looking at the pictures being used). It may be that they a) got permission b) they feel that there use qualifies as a "fair use." They do specify that theirs' is a non-commercial use (presumedly for educational purposes) HOWEVER the credits section does ask potential copyright holders to get in touch if they take issue with their use. I am not saying that they are making "fair use" but it seems like they are doing what they can to indicate they are and to avoid claims of infringement. (Their attribution to the original photographer does not lend itself to any fair use right they might have -- but is probably done out of courtesy). I would recommend you speak to an attorney to find out if there is an easy way to get permission or license the content you wish to use. If you are making a noncommercial use for educational or other purposes that MAY be afforded some Fair Use protections that would be something you would also want to discuss. I hope this was helpful and added something to the original reply.

You may want to organize as a legal business entity. You will, at the least, want to have a partnership agreement drafted. This is a difficult one to give a blanket answer on as more would need to be known about the parties and their objectives. I would highly recommend consulting an attorney before proceeding.

A combination of words may be trademarked but that does not protect the words individually. "Lean" or "startup." The focus of trademark law is not protecting the creative work of the owner but protecting consumers- preventing the likelihood of confusion with other recognized products on the market. Whether or not your material would infringe copyright would depend on whether or not you expressed ideas similarly ( not just having similar ideas). If you have Tm or copyright questions fell free to call me for a consult.

Whether you "need" to or it is advisable are different matters. I agree with the original reply and would add that when you say "we" it makes me think that more than one person is involved. Yet, another reason why incorporation would be highly advisable. There are numerous scenarios where you might later wish you had taken the time to incorporate or form an LLC. Clearly you aware of several given your concerns that you list about liabilities. I will go a step further and suggest that you not go "the one-size fits all route" of online legal services and spend a comparable amount of money speaking with an attorney to make sure that your interests, business model and objectives are accurately reflected in any operating agreement that is drafted. Feel free to contact me, I can answer any questions you may have and ask you a few additional questions that may help you make a decision whether this is something you want to deal with sooner rather than later.