The complexity of an online map is widely dependent on several things; first being what api/platform you want to use (CartoDB, ArcGIS Online, Google Maps, etc...).
What API/platform is best to use will be at least partially dependent on several other factors though, such as what licensing restrictions you can work within (ex: most of Google's api's generally say you can use it for free if it's under a certain number of api calls per day and if it's publicly available - not behind a pay wall).
Additionally, this is all determined by the level of complexity necessary within the map itself. If you are simply wanting to take some data (ex: a list of addresses) and put them on a basic, intuitive, webmap where people can zoom in and out and click on the points for more info, then that is not very complicated at all and you could completely do this yourself with pretty much any API/platform. However, if you are wanting to do on the fly sorting of data based on user input, that has some minor level of complexity in most APIs, but could still be figured out most likely. On the other hand, if you are trying to do some back-end on the fly processing (ex: when a user clicks on point X, it finds all the other businesses of type Y within # miles driving distance and sorts and color codes them based on user submitted review rankings). That starts getting a lot more involved. Please note, all of that is very much possible, but being able to write it yourself as a novice would involve a lot of time, trial, and error and/or limit you to certain APIs/platforms that are a bit easier for the specifically required functionality.
I know you don't want to give up too much information to protect your idea, I get that, and I hope this answer helps, but if more information was provided about the desired functionality of the resulting map, more detailed suggestions could be provided about which APIs/platforms may meet your needs best and then how complicated/easy it may be for a beginner to prototype.