Welcome Stuart. I'm just down the road from you near Stourbridge. As an ex-toolmaker you must be pretty skilled for starters as I know how demanding that sort of work can be (my late father-in-law was one).
Building a band saw? Is this purely an initial idea or a specific project. The reason I ask is that if it's for just general cutting metal for other projects have you considered it may be better to look at buying one of the quite modestly priced ones currently availabe. If you do a search on articles on this site you'll come across many recent postings on the topic – including often quite reasonably priced versions purchased through Aldi & Lidl!
I obviously don't know your personal circumstances re finances, but it may be worth looking into the real cost comparisons of all the raw materials you will need versus the sort of thing I mention above.
In the past, I've learned that in many cases, when I have made workshop equipment they rarely come up to scratch compared to good commercial items (perhaps its just me? ) OK if its something unique, or beyond the normal depth of my pockets – fine, I'll have a go. but generally I prefer to use tools and machinery to make things of more direct interest to myself. Not many people will consider making a lathe or mill from scratch would they?
Anyway, whatever you decide to do, enjoy! You will always find a wealth of useful information and helpful folks herein.
All the best. Mike