Yeah, this is what I did for my game last year. Whenever you get an error you have to look at the combined output to figure out which function it happened in, then try to correlate that to which file in the split files contains that function. I found that this was a bit of a headache once we got to over a thousand lines, and I wished that we had just used a single file for the whole thing. In most Fennel projects you can use the module system to split up the files, but TIC doesn’t let you do that for minimalism reasons.
Also one other gotcha is that the latest master version of TIC uses Fennel 0.3.0 while the stable builds use Fennel 0.1.0, so unless you build from source, you won’t have access to the latest Fennel features; this could be potentially rather confusing. The documentation from here may be useful: https://fennel-lang.org/v0.1.0/