As most Access courses already contain level 2 English and Maths (GCSE level / equivalent), I would say there is little point doing separate level 2 courses alongside the Access course because you will just be duplicating the work. Some universities will not accept level 2 equivalents and insist on actual GCSEs - although this is unlikely. You should check with the universities you intend to apply to now, and if they do want actual GCSEs it would be worth taking those alongside the Access course.
If you are doing Access to Science then obviously you will be covering level 3 (A-level equivalent) Science subjects. However, they will start you off slowly with easier stuff and then move on quite rapidly. You absolutely MUST ask questions straight away if you don't understand something, because the course moves on in a hurry and the same subjects are not covered twice.
Keeping on top of the work load is the key to success in my opinion. Not having any previous qualifications should not be a barrier, as long as you stay motivated and work hard.
At my college you will get help if you are working hard but still struggling, and the teachers are generally helpful and dedicated to getting everyone through the course. Don't expect to be spoon fed and have your hand held throughout though, a bit of independant learning is required to do well......... (At my college the number of people who seem totally unable to find solutions to very simple problems by doing 5mins of google or library research is shocking!. The first response to any problem is *I can't do it* and *ask / blame the teacher* - these people struggle).