I don’t yet have a Norns and have not yet started to code with lua but from what I’ve gathered -
how similar is its language to teletype?
I don’t find Lua hugely similar. if you’re familiar with a coding language like JavaScript or Python, then you will likely be able to grasp the concepts of functions, loops etc quite rapidly. But your knowledge gained with Teletype will be valuable, as the trick with coding is to develop a sense of computational thinking rather than worrying too much about syntax. With Teletype you already have a head start there.
and is ‘crow’ the bridge being built from norns to modular?
It looks like it will be - https://github.com/monome/crow is a good place to read up on it, but you may want to wait and see when it is released!