Is it possible to write a successful EA?
What does the code of such an EA look like?
Are there common design patterns / sections / tools that successful EA's share?
Do they all use the 'standard' indicators that come with MT4, or custom/proprietary EA?
Do you need to a successful manual trader in order to design/write a successful EA?
As a someone with developer background, getting to grips with MQL is not that hard. The hard part is knowing what to use/which indicators/etc.
P.S. - is this the right forum for these sorts of questions?
You may see that most of the signals of MQL5 signal service are from EAs.
There's also plenty of such topic in MQL5.com, one of them is Is it possible to write a profitable EA based on Technical Indicators?