#1. It depends with whom you're starting the venture to begin with, but in most cases it's a bulk deal negotiated on a percentage basis of your NGR (Net Gaming Revenue). Rarely there are one-time fees in this industry, and the crucial parts of the puzzle (e.g. providers) are usually taking a chunk of your NGR. It's important to note here that you can further negotiate the deal with slots providers depending on how much traffic you're getting. Some providers will give you a better deal if you're featuring their games on your homepage.
#2. They earn from your bonus budget (e.g. if you offer a $100 welcome bonus, you have to pay that bonus cost to the provider), and a percentage of your NGR. If you want I can talk with our casino manager and give you more details with some numbers here.
#3. If you're serious, you don't get it from Themeforest or TemplateMonster, that I can assure you. Usually you get a pre-developed theme that has been proven and tested by the providers that you choose (e.g. the platform provider). You can check out platform providers here, they have a full list: https://www.igamingsuppliers.com/suppliers/online-gaming/platform-providers/
#4. Yes, you have to have a bankroll, otherwise the license giver will not give you the license. Basically you need to be able to cover all the jackpots and large winnings from scratch. There is no "bankroll provider", but there are investors who are already within the industry and are looking to invest into new casino concepts. So if you have the team and the idea, they can finance it. But if you only have the idea, no team or experience, then I wouldn't recommend pitching at all. Banks will not be open to loans that I can tell you from experience.
#5. These are usually custom priced, and depends on the provider. There is a monthly fee due to the nature of the service (e.g. bookies), there's a chunk of your NGR again, and there are sometimes entry/yearly fees, it really depends on your traffic. Check out Betsson's solution, they have a really good sportsbook system, but I think that they only work with MGA licensed brands (I'm not sure).
If you're serious about the industry, I would recommend that you join one of the european igaming events like SIGMA, ICE, NEXT and others, I can even get you free tickets if you need to - networking is everything.
This was a great answer SirJohnVonSlotty, thanks for your words and your dedication, as you mentioned, lot of answers were just spam, but your answer was what i was looking for, so, now i will close the thread. Already leave my last merit to your post.
I really would love to see some numbers to have an idea about how much it really costs, but you are right, it's based on different factors like traffic and site popularity, but at least now i have an idea about how it works. Thanks.