Obviously you are discussing with the team, and getting ideas from everyone, to come up with the best outcome.
Just a thought.
You could make tc-install into an extension, and make dosfstools-3.tcz, syslinux.tcz and perl5.tcz, dependencies.
Unless something changes in the future, dosfstools-3.tcz, syslinux.tcz and perl5.tcz, don't have dependencies. When downloading them manually, you don't need to include .dep files, which makes it easier than apps with a lot of dependencies.
Most people won't need perl5, so would only be a matter of downloading 3 files - tc-install.tcz, dosfstools-3.tcz, syslinux.tcz.
The way I do it, you would only need tc-install.tcz and syslinux.tcz.
Another option is to combine them all in a large extension. You would only have one file to download, but then you have the same extensions available on their own.
I think using the existing App Browser, including Install Local, will be easier than making a new installer for tc-install.gz. Can tc-install.gz be loaded after the operating system, like Install Local?