First thing: Start small. You need to know how to walk before you can run. See the tutorials and the predefined templates to get to learn C2.
Q1. Don't rely on resolutions, use aspect ratio measurement. I recommend Scale outer mode
https://www.scirra.com/tutorials/73/sup ... reen-sizes
https://www.scirra.com/tutorials/1126/m ... le-devices
Q2. Not sure, try to keep it around 100~200MB on actual devices. About optimizations, there are a lot of ways, use google, or search the forum. Remember that bigger sprites/images use more RAM memory. Also music/sound files are memory hungry. And you will need to optimise a lot on mobile devices.
Q3. I've tried a lot of ways, at the moment it seems that you can't get constant framerate in any exporter. In my opinion Cocoon seems to run the best , but this depends on your device.
Q4. There are a few games published (some even on WiiU). Is up to you to judge.
Q5. Yes, Mortal Melon was made with C2.
Q6. Ads depends of vendor, if C2 has or not a plugin for that ad company. I've never tried IAP so I can't tell.
In my opinion, C2 is a great software and you can learn a lot about making games, but if you are serious about making bigger and commercial games, you should search for another software. You missed a great 12$ Humble Bundle if you knew a little programming.