Even with only a single map_fe.tga file and no faction-specific versions of this file, you can still get the same crash in the menu if you have enough additional elements, such as custom battle images. You must limit the total number of UI elements in these menus or you will get a crash - using a single map_fe.tga with a low number of custom battle images or etc. may be enough for your mod.
I use regular counters as integer variables (0, 1, 2, 3...) that only need to be checked within campaign_script. I use event counters as boolean variables that can be checked in other files (EDB, EDCT, EDA, standings, etc.). I sometimes use event counters as integers as well, just remember that EDB only takes values of 0 or 1. Event counters don't need to be declared like regular counters do, but it is good practice to declare them using set_event_counter anyway (there are tools you can use to edit a campaign save file but you won't be able to find your event counters unless you've declared them). I've read somewhere that event counters don't work on the battle map but this is incorrect - they certainly work for battle scripts in campaign_script. I'm not sure about export_descr_advice-based battle scripts, as I've never done any scripting in that file, but I have seen I_EventCounter used there as well.
I spend about half an hour trying to crash the RotK menu - didn't happen, unlike with 18+ factions enabled. It does support the reports that the more factions (and their maps) you have the faster the menu crashes. There is an article somewhere where someone went in depth into this issue, possibly the miscellaneous section.
Custom battle images take two\three steps back from the faction selection screen, not sure if that actually crashes. At least I haven't heard of it - usually the crash happens if you keep on clicking on factions in the faction selection screen or if you go back and forth from there. In all three locations: default campaign, hot seat campaign, custom campaign.
My mod uses a single map_fe.tga and still crashes with 27 factions in the menu and around 30 custom battle images. I "fixed" it by replacing most of the custom battle images with a single file, but it's still possible to crash the game by furiously clicking buttons and switching between menus. All we can really do is make it harder for the user to ever induce this crash by limiting the number of UI elements on various menu pages.
I don't think it matters which menu pages you're switching between or if you're switching at all - loading a new page just makes the crash happen faster because you're loading a whole set of new UI elements into memory.