I chose my school based on location (although a location I do not like as much as I thought I would). Beyond cost, I would evaluate course load, test schedule and available resources.
Given my learning style, I wish I had gone to a place with a block schedule rather than a school with several tests every week as I need at least a mental half day of rest. I also would have chosen a school with more non-trad resources and less fluff to the cirriculum (worthless classes and activities that take away from your precious study time). Ideally, a place that allows you to transition back to school (my gfs school allowed them to take anatomy over the summer and have a lighter load in the fall first yr. I did not get into a school like that but it would have helped me a lot). Finally, a smaller class size would be nice. In both my high school and college I knew most people but do not now.
I feel you on both these points. A lot of times I feel like a fish out of water at my school and I can't blame anyone but myself. I choose the school, I had other options. I am slowly hitting my stride, but overall it just sucks. At least admin has been decently supportive, and gotten me tutors for my weak areas. And I finally have a study partner that's on my level (i.e. nontrad with family that doesn't have a previous PhD, masters, or some nonsense like that). I hope you do well!
And to the OP, I would very much agree with other posters that the 4 year completion rate is probably in the 80's for most DO programs (although the actual attrition rate, i.e. actual loss of students is lower). Just be glad that they don't just kick you out. Most DO schools at least try and support you. Well, at least mine does. IMO you are going to a DO school instead of the Caribbean because they will actually care if you are failing. They might force you to repeat a year, but at least you only pay for the classes you failed (I understand this is a federal thing, so should apply everywhere). Most Caribbean are happy to let you fail, recharge you, repeat and then fail out.
I think its important to read the Student Handbook and see how a given school deals with these issues, cause its really one of the most important things, if not the most important. Sadly not everyone can be 'above average' in a class with hundreds of people (especially a group of people who were for the most part, very above average in undergrad). That being said, prepare for the worst and hope for the best. If you can get in, you are probably capable of completing.