How does this compare to Spotify which has 3000+ employees, debt financing of over a billion dollars, and an insane valuation? What does the future hold for that company whether it IPOs or not?
Jokes aside, having to negotiate with tons of artists and their labels/managers, I imagine their legal/business department is significantly bigger than that of most tech startups.
AC/DC, Led Zeppelin, the Beatles and Taylor Swift come to mind, but there are very few artists who have a say in whether or not their catalog can or can not be streamed. Those artists made wise business decisions at some point and/or were able to throw their weight around. Here are some notable hold outs as of 2016 anyway:
https://consequenceofsound.net/2016/02/which-artists-are-sti...
Using Pink Floyd as an example, the decision was there's and not their record label EMI:
http://www.rollingstone.com/music/news/pink-floyd-catalog-ar...
Because if they want to have support at all (unlike, say, Google), they need quite a few employees.
You need sales people to sell ads, designers to build out the creatives (assuming the company you sold ads for doesn't have media that fits with your platform). Then you need account executives to manage the account. Then you need a billing department that collects the money. Then you need engineering to build out your ad serving abilities.
For IT you have the core that builds what some here have called a "shitty" UI. Then you have people working on all kinds of invisible things like developer tools to support releases. People working on recommendation engines. People working on instrumenting data and metrics for business analysts.
Then you have people who hand-curate music for each of the markets and local tastes that Spotify operates in. Then you need people to manage these people... Etc.