Is it enough flash?

Hi there,
I have an TP-LINK MR-3220 (4/32 device), with custom BarrierBreaker (removed all PPP, IPV6 related stuff, added MWAN3). Works OK as failover (from main WiFi to backup WiFi - phone with "tethering").

I have now 196kB flash free. Is it enough to (re)install all things needed for 3G connection? I'd like to add 2nd backup link, not dependent on presence of my phone, just USB 3G modem and a SIM.

I have an Huawei modem (proven to work on laptop with Fedora), so I think I need: kmod-ppp*, kmod-option, usb-modeswitch, and pppd.
Should it fit? If no, is it possible to place "/overlay" on an external USB flash?

I suggest, you first use all possibilities to reduce amount of flash required. Which means, to build a custom image (18.06.5, I suggest) without kernel debug, no opkg for example. There are quite a few other options. I am shure, then 3g should fit.
The build process will not generate a flashable image, in case it is too large for the 4MB.
So you are on the safe side.

Ooops, failure even with (slightly) modified .config from my working config (Barrier Breaker 14.07).

Just added PPPd, PPP kernel modules, modeswitch, etc.
But adding ext4 and usbstorage, ser2net, serial drivers (other than option/wwan) was (I think) too much, now trying to build them as modules, maybe this will free enough flash.

OK, it build at least. Will flash image probably tomorrow.

Is it possible to attach files (",config" in my case) to the thread or have I to put it "somewhere" and paste only URL of?

kmod-fs-ext4 is big. For an extroot setup it is common to set up the internal flash with only enough to get extroot mounted, then install additional packages at runtime. Space is not an issue as they will be saved on the external drive.

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OK, flashed my new firmware to "spare" MR3220 v1, works (at least tested as AP + WDS client + bridge, no routing task for now). LuCI works, settings kept.
And WOW, it shows 352kB flash free :). With kmod-ppp*, pppd, mwan3 already in flash. USB storage, EXT4 in ipk files on PC.

Will upload .config somewhere and put link here.

Here it is: GZIPped .config .

Maybe there is some "intermediate solution", between internal 4MB flash and extroot? USB flash with 2 partitions, one small (megabytes) FAT to hold only kernel modules / tools for EXT4, and another EXT4 for "work"?
What do You think?

Drop LuCI. Then all will (most likely) fit into flash.

I am not Debian / OpenWRT config files "master", so at first I try to configure (especially new) things using LuCI. Only then try to understand syntax / make changes.

Is there some "step by step guide to OpenWRT configuration"? Ie w/o LuCI, config files syntax and their interrelations?

BTW I am sometimes surprised: I'd made changes to /etc/config/wireless that WORKS, but LuCI drops "WiFi" menuentry from "Network" menu, AND "Network/Interfaces" shows some interfaces (WiFi STA as separate interface, fixed IP) as "Unsupported protocol"... In this case I've configured one WiFi as AP, other as STA, now WDS, separate interface (for routing not bridging).

I either use Luci or config files directly. Not both. Config files either to be modified using uci or to be edited directly.

So question is: