I think what is "doing enough" for each person is highly individual. My Mom passed away from a lung disease about 2.5 years ago. I was willing and able to spend time with her, take her on drives around town, and help out in whatever ways I could. But there were things that I wouldn't feel comfortable helping her with (she was very frail at the end of her life) and things that perhaps if she had asked I would have said I was unable to do. I had two sisters who lived out of state and they visited more often the last year or two of her life. But we weren't there 24/7 and we didn't drop our own lives to be there all the time. What each of us chose to give and do was enough. I think it's OK to have limits on what you can or will do for your Dad. Don't pile guilt on yourself where there really shouldn't be any. If your Dad guilt trips you, you need to work through that regardless of when he dies. Also, no matter what you do, it won't be "enough" in the sense that he will still pass away. But that's different - that's just death. It's not a reflection on you or if you've done right by your Dad near the end of his life.
I do have a few suggestions. First, talk with your Dad's doctor to see what the prognosis is for your Dad in his current condition, and ask for the doctor to be straight and honest with you. Most doctors are able to talk about death and dying, but many aren't. If you know your Dad has two months or six months or a year, that can at least give you some information on which to make reasonable decisions. If he is in the last week of his life, maybe you take the week off from work under FMLA and stay there and fly home in two weeks after the funeral. If he's got another year, maybe you fly home tomorrow and promise to visit at Thanksgiving or Christmas or Hannukah or whatever.
Second, there are other options besides living with/at your Dad's or a hotel. Check into VRBO or AirBnB, you can cut that cost in half. Similarly with transportation - maybe it would be cheaper/better to drive, take a bus, or take a train. Or if flights make the most sense, see if you can travel hack yourself some free plane tickets.
See what the doctor says, but even if your Dad is in his last days, you can still decide to stay at the hospital but take a walk around the building three times a day, or whenever the nurse comes to check on him, or whatever schedule you set. You at least need to take care of yourself enough so you can be strong and able for him and whatever he might need. So this includes things like getting decent sleep, exercise, food, and stress relief.
I'm not sure if it would help, but maybe also talk to the doctor about your Dad's living will / durable health care power of attorney. If you have that, it might be possible to get your Dad into hospice. Again, hospice is a very personal decision for an individual and family, but my Mom was on hospice the last year of her life and it was superb and excellent and worked out really well for her. I would highly recommend it.
Good luck.