It's pretty hard to answer your specific questions.
1. I guess the living standard in dorms really depends on the city. And even where I live the standard is very diverse between the different dorms. Also the rent mainly depends on the city. I would suggest to get in touch with the university of your choice and ask those specific questions regarding the living situation there.
2. How much you can earn is also really specific. I guess you can expect a pretty good hourly fee as long as you can find a employer who speaks english. I have no idea how the market for english speaking programmers is. Your best shot is probably to work as a freelancer over the web.
No it is not. But there are indeed few Masters programmes which are instructed in English.
The University of Göttingen is a good example.
http://www.uni-goettingen.de/en/40954.html
As long you want to study at a public university there are just tuition fees which have to be paid once per semester. How much you have to pay depends on the university, I'm currently studying in Osnabrück, Lower Saxony and here we pay around 280€. But the fees include a ticket for the local public transport and you get to eat a lot cheaper at the university restaurant.
Regarding living costs I would say I need around 500-600€ each month including rent. If you wanna study in one of the bigger cities you probably have to add another 200€ onto this.