1. Surprisingly, the United States Human Service Psychology programs are telling the truth when they mention that they try to look at the applicants holistically. However, your low GPA will hurt your application package. Sometimes, the application process is simply a number game. Suppose you try to spread your application to as many universities as possible. In that case, you might accidentally hit a university with a slightly lower number of applicants in a particular year, and you can get into the program because the amount of competitors for the PhD seat is pretty low.
2. American universities certainly appreciate UK master's credentials, especially those from Russell Group universities. It never hurts to try the UK's Clinical Psychology doctoral program, and the NHS funding is pretty generous for UK citizens.
3. I am not sure a master's degree in philosophy can be a research-focused program, except if the program offers an Experimental Philosophy focus. However, the Clinical Psychology Selection Council will appreciate any writing samples showing how you generate research ideas. It would be better for you to write something interesting during your time in the program. Also, you should consider Duquesne University's Clinical Psychology PhD program. It was rather unique as it is probably the only university website that clearly mentions philosophical inquiry. Moreover, the entrance essay for the university focused more on philosophical writing, so this particular university might really value your experience of doing a master's degree in philosophy.