See https://feather-wiki-external-core-demo.tiddlyhost.com/ .
It’s a demo of an “external core” style Feather Wiki on Tiddlyhost. Click the link above for more info, and to try it out for yourself.
A brand new empty is 714 bytes. It does grow as you add your content though.
One question to ponder for TiddlyWiki hackers (making sure this is on topic… ) - An external core TiddlyWiki is still 107 KB. Could it be smaller? How and/or why not?