Hi,
As you said " I find this era of Leica photographs to be very interesting since people are still learning how best to take advantage of the small camera." I'll add a few to the list for you, I hope the luxury fund can cope.
The Hove Foto Book reprints of the 1931, 33 and 36 Leitz catalogues are brilliant to get the feel of the cameras and as a data source. Dirt cheap here in England and no one buying them on ebay, IMO. Sometimes you bid on one and get the original and not the reprint! BTW, they were intended for dealers only and a series of simple leaflets were available to us riff-raff that are well worth collecting.
There's "The Leica Data Book" by Karl A Barleben from 1933. It seems that he was organised and had a scrap book or note book of useful tables etc and put them all in a little book. Originally 50 cents but probably more these days. Sounds boring as I've described it but really absorbing.
Back to Leitz booklets; there's "Leica the Camera of Modern Times" and "The Interchangeable Leica Lenses" both come in several versions for the USA and Great Britain. The differences between them being very interesting to me.
There's also (rare) "First Principles for Leica Users" from 1935 and it's a sort of conversion course or "a concise introduction" to modern photography. Expensive (sometimes) but 2 sheets and 2 staples making a neat and interesting 8 page booklet by Leitz, of course.
And there's this:
And there's that big fat book "Leica Literature 1930 to 1960" by James Lager. And, at the other extreme the little cards they put in the pocket in the back of the ERC like the exposure tables and export/import certificates.
I hope that keeps you amused. It'll keep you poor, guaranteed.
Regards, David