I grew up in shops and I will recommend them first all day long. I do also recommend looking into the Priority Continuum. It is a bike that has many features that you cannot get for the price at a shop. It also checks your boxes and should not have issues with your terrain. I would recommend that if you do not know how to build a bike please find a shop to bring it to. They may charge you $50-100 but it is best to have it put together by someone who knows what they are doing. It is not hard to do but if you have any doubt bring it to a shop. https://www.prioritybicycles.com/products/continuumonyx