The biggest problem that I was facing in my startup was collaboration and being on the same page as others. So as a founder I got in touch with @nilova_pande and she shared me about Qinaps . I am using Qinaps since 4 months now and I am very happy with the service. You should really try it out.
being on the same page may be a challenging as your team may be across the globe and all come from different cultures. It's useful to take into account the cultural aspect to ensure effective communication.
The biggest problem is to make sure that you are paid properly for your work hours. What helps my team and me is using TMetric time tracker to log the time and then bill the clients accordingly.
Also, it's important to stay in touch together for discussions and meetings, and since we all have flexible schedule we've agreed on having online calls twice a week to learn what tasks and projects everyone is working on and if any problems arise.