There are a lot of questions which need to be evaluated, not the least of which is what the overall size of the market, and is it expanding or shrinking? How many customers are there? How much competition is there? Are there any barriers to entry? Is there a possibility of new entrants increasing competition, or providing cheaper substitute products? All of these things need to be considered before you begin to invest in a new product or service.
Bear in mind that this is similar to starting uk email lists a business from scratch, even if it is in an adjacent market. Yes, you may have considerable ongoing income, but moving into a new area has its' costs, so you need to know whether or not it has sufficient potential before you do so. There are other things to consider such as technological developments, changes in government rules, economic indicators, and so on, and today such things as the impact that coronavirus will have on your future business.
All need to be taken into account, and a market research company can be of considerable help. Starting a business from the scratch is no easy task. It takes time to register your business and get all the proper licenses. There are many overlooked steps that every business should take to be successful and you won't find them on "how to start a business" checklists. The following steps might seem like an additional investment but in the long-term they will all pay off.