I recently completed L1, L2 and L3 (including Self Assessment and Payroll). I used Ideal Schools as my training provider they were fantastic (contact Brian at Ideal Schools he will be able to help). I passed all my exams first time mostly with distinctions. I completed the course in just over four months (all the levels). So it can be done!
I would say that a Training Provider is a good route if you can afford it. Level 1 is quite easy, and if you are reasonably competent in numbers and basic accounting principles it's not too daunting. I would say that Level 3 is most challenging, but not insurmountable.
The key to getting the qualifications is not to leave a large gap between the exams as you will forget things from previous levels and will need to recap and that can be tedious and time consuming.
Also, I believe that the key to learning the principles of book keeping is practice, practice and more practice, until you understand the principle. Don't get bogged down by the need to understand everything too deeply at the outset, it will come with practice and doing examples and exercises.
I hope this helps. This is just my experience and everyone else here will have a different experience and approach.
Are you looking to set-up as self employed?
All the best in which ever route you take!