If I make my own design, but it's too similar in concept to another site, can I get in trouble? For example, if I place similar elements in similar places and if I have a similar sales funnel, despite all the content being different, can I ever get into trouble for it?
Good question and impossible to answer well since it's an analysis of the specific facts on a case by case basis. As a general rule, I'd use a sliding scale. The more complex something is, the greater the chance that a higher level of copying or replication might be considered infringement. How elements on a web page are spaced or arranged - unless it's extremely unique and highly detailed, I doubt that general organization can be protected or even semi-common processes. If you do replicate the overall look, certainly don't copy the code they used to create the arrangement (copyright law). Sales funnel is the same - unless there is some patentable process, which is extremely rare in most cases. Note that there is copyright protection for "look and feel" but such cases are rarely made and the replication required is usually great. Someone might not send you a cease and desist letter, which may just be a scare tactic. Proving these cases is difficult and the only person who can say for sure whether something is or isn't infringement is a judge.