Hi, i admire how you really want to go back and work for what your dream is! Good on you!
I just sat the L.C last year,biology being my favorite subject, and like you i also attempted to get into medicine,i didn't but im doing science and then hopefully post grad medicine will work out.
I think that you'd be well able to study biology at home. The books I used were discovering biology-it was easy to understand and it had a dictionary at the rear,i also used the revise wise for biology. If your at home you'll need to be able to either understand FULLY the experiments on the course or somehow actually do them which can be hard for some.. i bought a lab prep book,its written by David Bourke,i had him as a teacher in lesson street. Its 10 euro and well worth it,have a look :
http://www.schoolbooks.ie/23873-Biology+Laboratory+Notebook+Folens+School+Book
The new course is really focused on experiments so that's important.
What id suggest is that you just work your way through the biology book,from start to end, chapter by chapter. Try to give yourself little tests after each chapter and whatever chapter you have completed make sure you do exam questions from previous papers on it! Go to examinations.ie for free papers on ANY subject.
Just have an open mind (like you seem to do) and work slowly towards finishing the book. The main Topics i would suggest you do and get out of the way are: The cell,DNA&RNA,Genetics,Genetic engineering,the human body ie. all the systems, osmosis, Darwin's theories, Ecology, Bacteria.
Hope everything works out, for extra notes or help you can check out these sites:
http://www.skoool.ie
http://www.sparknotes.com which is AN EPIC SITE!!! 
and google itself ha!
Good luck!! 
