Sheeesh. I haven't got time to waste replying in detail, but if others still want to comment on the thread, I want to be sure they aren't misled. In case they also don't read the thread properly.
My question is not asking how to do the project. I hope it's obvious that there is no short answer to that question. As I said in another post, I don't have all the answers, but I have the knowledge and experience to work my way through this. As previously said, that includes database knowledge and experience.
This thread was about getting other people's views on the relative size of the project. I had my ideas, but I'm not perfect, and there is much more MS Access experience on this website than I have. The gist of the comments have supported my initial estimates, and the one reminding me that all projects are 2.5 times bigger than originally estimated was very appropriate.
Nothing to do with luck. I'm racing along enhancing the thousands of lines I inherited, addressing the issues raised by others in this thread, and addressing plenty more.
I'm beginning to get some engagement from the business, which was one of the missing pieces. I take that to mean that the users are seeing progress, and are beginning to see why this system was introduced by the manager who has since left the company.
That might not be the case, but I'll continue working with the company until there are no more benefits to be gained.