Three interesting questions
1)How much money do i have to change before to start the 14 days trek to Everest Base camp ?
Answer (updated in January 2019 from what you are going to see in YouTube): minimum 500 dollars if you will not drink alcohol during the trek, more if you will, however i advice you not to do so, enjoy the trip live the moment the now with your entire feelings, let alcohol for celebrating the end of your trek, extreme cold and alcohol are very bad combination and will harm you.
Why minimum 500 dollars? for example the price of the water varies between one dollar in Kathmandu to 3 dollars or more in Lobuche. Batteries charging price varies between 3 dollars all day in Namche Bazaar to 3 dollars an hour in Lobuche . This is normal because after Lukla , transportation of the food and material is very expensive for Tea houses to procure. The money can easily be changed in many currency exchange places in Thamel, take your time to find the interesting offer.
2) What about packing list ? i brought everything i needed with me, i did not buy any further gear from Kathmandu
3) ATM , credit card ? No, i had cash π