If you are living here, you are entitled to NHS services. (Heck, some people on here have been treated by the NHS while they were here on a tourist visa!) As far as dental, you have the option of going to a "regular" dentist or an NHS dentist. You have to register with an NHS dentist, and some may not be taking on NHS patients, so there may be a waiting list. You can always go to a regular/non-NHS dentist for treatment, but you'll probably pay more for the service.
It's been my experience that doctors will find the closest equivalent to whatever drug you're taking. My only experience has been with the Pill...when I first came here, I was on Ortho-Cyclen, and the doctors had never heard of it! So, they looked up the active ingredients and prescribed me Celeste, which is really the same thing, just a different brand name. Chances are the same will hold true for your meds.
Some employers do provide private medical coverage, but the vast majority don't. I don't know about the cost as I just rely on the NHS at the moment.