Could be a bit short, depending on how much booze and partying you want.

• A 7-day pass for public transport is less than €40. Together less than €200. Depending on the timing of the Bonn trip, you might need only four weeks.
• The train return ticket is around €130, depending on how early you book.
• Food is possible for €15 or less, especially if you can use your friend's kitchen and fridge. It makes a difference if you buy prepared sandwiches or bread, butter and the rest.

That leaves €220 for the other points you mention. Museum tickets and nightlife can be expensive. No idea about the SIM card for a month.

Could be a bit short, depending on how much booze and partying you want.

• A 7-day pass for public transport is less than €40. Month passes exist for calendar months or 30-day periods, a bit over €80. I'm assuming that the Bonn trip will be in the middle of the visit?
• The train return ticket is around €130, depending on how early you book.
• Food is possible for €15 or less, especially if you can use your friend's kitchen and fridge. It makes a difference if you buy prepared sandwiches or bread, butter and the rest.

That leaves €220 for the other points you mention. Museum tickets and nightlife can be expensive. No idea about the SIM card for a month.