I wrote most of the advice I had to give here: https://feuniverse.us/t/reflections-on-romhacking-lessons-i-wish-id-known-going-in/23668
I might add to it eventually.

I've been trying to think of a more interesting answer to the second thing for several days now and failed. Really, I just want to see more focus on story in general, with settings that feel thought-through and significant (without just devolving into Worldbuilding (derogatory)) and more of a focus on nationhood. I think you can put a lot of different stories into an FE framework, which when you get down to it is really just 'a lot of skirmishes', and there's some I've absolutely not thought about.

I knew what I wanted for E-3 quite early in the process. I knew I basically wanted a closed castle against 50 elite enemies - the only chapter in the game without unpromoted enemies, as it happened - with minimal reinforcements, attacking through two sides until hitting the centre (originally the dead centre, now of course the top). The concept had actually been in my head for several years, in my mate's playthrough of FE4, where he remarked that Julius Plus The Dark Warriors was - actually getting Julia back notwithstanding - actually a very strong final boss encounter, embracing that Julius himself is basically a procession if you get to him with the right person, allowing your star to push into the base while your lesser lights run interference. What could have improved it, he said, was making them respawn. So, that concept of 'relatively easy boss battle but respawning Dark Warriors' was in my head for years, and was always going to be the final battle; I'm pretty sure it was in the original list of 12 chapters, too.

It's actually the author's. I can't abide moths or butterflies unless they're completely still. Something about the way they flutter in unpredictable patterns around face level.

In-text, Roxelana's arachnophobic, but has pretty rational reasons for it having seen a few of the man-eating ones up close and personal. In-me-making-up-something-right-now, Clio's got the 'afraid of holes' thing. She shudders violently at the sight of paper-wasp nests. But it's not a well-documented thing in her experience, so she keeps quiet about it.

It's not a phobia, exactly, but it's deliberately brought up a few times in Do5 that Rena's very fastidious and hates dirt, mud and general grime. If she can't wash or has to sleep on the ground, she's going to be very on edge.

Sat on this one for like a week trying to think of a more interesting answer, and failed.

Honestly, they were only ever going to be custom campaigns. DoW was made because I had my own ideas about what FE should look like and what space it could explore, including a story that was built around having relatively light scenes between skirmishes every so often; Do5 was only revived because it existed in the first place. They each share some similarities or occasionally elements with other work I've done, and occasionally characters are further examples of recurring archetypal characters. But, really, the identity of each can't really be uncoupled from their identity as Fire Emblem campaigns, and it just made more sense for me and for the things I wanted to work within FEBuilder, not LT.

That said, the very earliest tinkering with making DoW was actually in Tactile. I didn't know FEBuilder existed, yet, and kind of assumed people were working with FEditor or tools similarly opaque without any backing in coding. This didn't get as far as, like, making maps or implementing classes, though.