Is Zscript usable in level scripting?

Yeah, you'll primarily be using ACS for map scripting. There was a fairly recent thread on the ZDoom forums about this, and suffice to say it's not likely that ZSCRIPT will supplant ACS like it did DECORATE for a while.

You can use ScriptCall in ACS to call ZScript functions from a provided class. This is useful for extending ACS beyond previous limits or accessing additional information (ie. the size of a graphic) that ACS was not capable of fetching previously.

Oh cool, I could potentially make a library of more complex things if needed in zscript.  But yeah it sounds like for basic things like an elevator I should be able to just do most things with ACS still.