4 layer boards aren't too expensive nowadays, but 6+ layers are considerably more. Also with 4 layers you have a reasonable chance that mistakes can be fixed with a cut and strap.
If I was designing this I'd probably go with 4 layers. One inner layer for 0V, the other inner layer for power...
For 74 series chips the following applies
The CD prefix was traditionally Harris but they were acquired by Texas some time ago. The E suffix on a CD part is the same as an N on a SN part. Different manufacturers may have slight differences in the performance which you can find by comparing...
1990 Sears Christmas catalog page 660 has the SR 1000 printer, it seems this was a Sears branded printer
https://christmas.musetechnical.com/ShowCatalogPage/1990-Sears-Christmas-Book/0660
They ar soldered into the pcb. Try searching for CR2430 tagged cells, Google only wants to show me uk suppliers but here's an example
https://uk.rs-online.com/web/p/button-batteries/1882133