NLnico. I am looking over your math and you seem to be within reason saying that.
Although, Depending on who you are hosting with bandwidth is "free" meaning it is included in the package.
Now don't get me wrong, I'm sure most bandwidth providers have un upper level on what they are willing to offer with packages..
That being said though, When you have a private show you can be raking in $500-$1000 for an hour or two of streaming.
Multiples of that private show can easily end you on the right side of profit even if you were to have outlandish bandwidth costs.
Actually my calculation seems wrong. 1080P video is around 5 - 9 Mb/s but that's megabits not megabytes. So let's say 8 Mb/s so 1 MB/s, then it would be 1 * 7200 * 1200 / 1000 * 0.03 = $259.2
$0.03 per GB is low though, that assumes that you will have petabytes of traffic each month*. $0.06-$0.12 per GB is more realistic. So price would be 2x259.2 or 4x259.2 still around $600-$1000 for 2h show I guess.
* based on CDN Fastly: http://www.fastly.com/pricing - just a random CDN though, probably not cheapest or whateverAlthough, Depending on who you are hosting with bandwidth is "free" meaning it is included in the package.
Now don't get me wrong, I'm sure most bandwidth providers have un upper level on what they are willing to offer with packages..
So then you would not take a CDN but a dedicated server and have streaming software on it (which will require some expensive software and more development.) And for the bandwidth, still you could make calculations. Most dedicated servers do have a TB limit, like 100 TB. You can calculate how many 1000-viewers hours that is per month. Also I am not sure if for example a 100 Mbit or 1 Gbit connection would be enough for thousands of 1080P streams (you can calculate this too though.) And then I am not yet talking about the hardware (which probably is more difficult to calculate.)
Obviously you would start with a smaller server too. But then again you can calculate it
Like if you have 1MB/s stream, 1 hour, 1000 viewers, 1000 MB = 1GB:
1 * 3600 * 1000 / 1000 = 3600 GB per hour. So 100 TB cap: 100*1000/3600 = 28 hours of 1080P streaming with 1000 viewers (assumes they all watch for 28 hours.)
Developing a site (without the actual streaming part) is not even that special. But you definitely have to look carefully into the hosting aspect. You cannot just get any "unlimited" hosting package, they will block you in a day, all covered in their TOS.
You will need to make an estimation of shows, hours and viewers per day. Turn that into a number of gigabytes. And check how much that will cost with several CDNs and dedicated servers. And if you go with a dedicated server you gotta look into streaming software, development costs, hardware requirements and connection speed limit. Ideally you could make an estimation for when you have 50 viewers, 500 viewers, 1000 viewers, 2000 viewers, etc. And also private shows / non private / lot of tips / few tips. So you can calculate the estimated costs / profit in the beginning and as you grow. And also in the ideal situation (lots of private shows + tips) and the least ideal (no private + few tips.)
EDIT: my math is probably still wrong, but just for example so you can calculate it in detail yourself.
EDIT2: Also remember that these costs should be covered by your 15% cut only (!)