In going through old HALion content, it looks like in the past, LUA was mainly used for making Macro screens.
I do believe it’s becoming a little more popular to use it for sonic purposes.
I don’t think it’s too difficult to learn really. What sets it apart from other scripting languages is that instead of dealing with lists or arrasys, each variable can be a full blown TABLE of sorts. So, LUA is really good at dealing with data fields 
It’s perfect for VST3…mostly what I’ve done with LUA so far is grab the value of existing parameters (we can see them in HALion’s Parameter List) and do things with those values before passing them on. It’s also pretty easy to declare a new variable.
A great place to start learning, is to dig around in the new Hot Brass, and Symphonic Strings that came with H6 for the acoustic/sample based concepts. Dig into flux for some ideas with synths. Go to the LUA for HALion page and explore the events and functions supported. Read a few LUA primers, etc.
I took a quick look at the issue of using an LFO to drive things that aren’t listed in the GUI as attach points.
For now, I don’t see an obvious way to get the data from the LFO’s output directly, but I’ll keep digging.
If that’s unsuccessful, it would seem that will be possible to attach the lfo to something that is specified in the list of options, but perhaps hook it to something that’s not really effecting the sound…then…snoop that parameter and echo it off to other things…say, a QC, which can then be easily scaled and attached to all sorts of things.