EFS ia a partition that holds meid, imei, serial number, config, diag settings and radio settings, etc l_modem is also a partition, but it's a
different partition.
You should make one backup, at first, with all the boxes checked - in other words, back up everything. (Do that every time you get a new version of Android.)
But other than that
do not fool around with any partition but cache and data. (If you mess up everything in the data partition, you can still run TWRP and restore it, but there are some things you
can not do. Someone posted yesterday that he was told to wipe
everything using TWRP. That includes EFS, boot, system
and TWRP. Now what? It's a nice motherboard, some silicon, and a case - it's not a phone.)
Use TWRP for backups, for flashing things that come in .zip flies, but EFS, l_modem and half a dozen other partitions? Back up only. Restore if needed. That's it.
(And see if you can find 3.2.3, or at least 3.2.2, for your phone. (
https://twrp.me/Devices/)