How to manually transfer entire Whatsapp installation to another device (the hard way)
I was encountering the crashing behaviour trying these approaches too, but @DeathMaskSalesman seems to've been on the right track—the crashes are indeed a permissions issue.

If you remove WhatsApp entirely, reinstall it, and copy /data/data/com.whatsapp over and adjust the permissions correctly before launching it the first time, then it should just need to reverify your number to work.  This worked for me.

To adjust permissions, first use ls -la to check the permissions on what's put in the /data/data/com.whatsapp directory upon install, e.g.:

drwxrwx--x   3 u0_a105 u0_a105  4096 2018-07-14 00:55 cache


Then use the username and group (here both u0_a105) to rename the files after you've copied them in:

chown -R u0_a105:u0_a105 /data/data/com.whatsapp/*


Then WhatsApp should launch okay without crashes, and retain settings, messages, and multimedia.