Be careful with this option.
I have done a lot of research on this exact method recently for my family vacation at the end of the year. Indeed you can book the different travel classes and add car and hotel, but the price was a lot higher for the overall booking as you don't receive a "BA Holidays" Flight and Hotel discount as you would booking it the traditional way.
I found booking it the traditional way and phoning them immediately after, (or doing the full booking over the phone) gave me the best results and pricing.
I also believe with BA holidays there is no change fee (usually after the first 24hrs this kicks in)
Correct me if I am wrong.
Good luck and I look forward to reading your feedback.
Colnic2011