You need a things how they will be work. So there is would be based how is your business work, How much about script, servers, license, office, regulation, team, promotion and etc.
online casinos do not have physical offices, so at least in this part they do not spend money, because to build a physical office costs money and not little money because it will depend on the location of the office and no one would build an office in a place with few people, everyone want to be in the city, where there are many people, about the team, without a doubt this is a headache, because the ideal is to always choose people from the real world that the person knows, and not choose random people from the internet
Many those casino work until now, they never sign message for they bankroll/funds able to paid to public.
on this issue and until the other day I was wondering if maybe some of these new casinos were running casino with low funds and as everyone knows that at the end of the day the casino always makes a profit so it starts to get high bankroll, it's just my suspicion or assumption
creating a casino is a process, you first need to research how much each step of creating an online casino costs, for that you need to ask several people linked to the management of a casino, after you know the amount you will have to spend so you have to choose a good team and with that team it will be easy to take care of everything