I'm having a very hard time finding what I need in an ad serving platform. Am I asking too much? Am I selling my space incorrectly? We get around 1.5 milllion pageviews per month and run AdSense in the zones as a remnant. - A user should be able to specify the number of impressions they want to buy as well as the time span in which they should be displayed. The software should be able to forecast how many impressions the site received, and then determine how many of each ad needs to be displayed in order to meet those goals. - Ad zones should be defined by permanent code, and then listed as available inventory options when creating new campaigns. - Software should be able to differentiate between computers and mobile devices, and then display the appropriate ads.
Considering your current scenario, I would suggest DFP Small Business. It supports everything you need (including AdSense built in) and forecasting, targeting, dayparting. etc. DFP Small Business is also free up to 100,000,000 Impressions per month - I believe. Any more questions feel free to shoot me a PM, happy to help.
Its actually extremely easy compared to alternative options. I have to be honest. If you need help with DFP - shoot me a PM, I can give you some help.