Good grief. Who in their right mind would ever collect handstamped cancels on 1st issue revenues? What a ridicul.... wait, what?

You are embarking upon a serious addiction that never ends. The nice thing about this specialization is that it can be as inexpensive or as expensive as you choose it to be. You can find wonderful examples on
ebay and other online sites, in APS circuits, and in dealer inventories everywhere... even in junk boxes.
There are very few references to cancels. The two most essential (in my opinion) are the Tolman/Shelleabear references on railroad and insurance cancels. Also worthwhile is Bruce Baryla's photographer cancel reference, but is in need of updating; the online version of his multi-award-winning "Civil War Sun Tax" exhibit is a reference work unto itself. Kristin Patterson's "It's a Wrap!" on playing card cancels is a must-have if you collect the 1st issue playing card stamps and cancels (which can get AMAZINGLY expensive).
There are some other references out there on steamship cancels and a few other topics, but they are descriptive only, no pictures. I am in the (slow) process of putting the Tolman references online at my website, and then possibly develop a reference on bank cancels based on material in my collection... but that's a task for 20 years or so from now when I retire.
It's an area sorely in need of reference material. Mike Morrissey keeps threatening to actually publish his research on proprietary cancels. I REALLY hope he does, as he is a treasure trove of information unto himself.
Other than the above, Eric Jackson's website and especially the auction archive can be good resources. Stampauctionnetwork.com and pfsearch.org can be good research tools as well. Start accumulating auction catalogs that featured early revenues (Cunliffe, Joyce, etc.).
That should be enough to drive you nuts for the moment.

Welcome to the insanity!