Tentative PhD Offer - What to Expect

I was fortunate enough to tentatively be offered a PhD position at ETHZ. However, I currently live in North America and don’t have EU/Swiss citizenship. They’d like me to start in January, if possible.

Of course, I’d like to get some realistic insights. How long does the visa and work permit process normally take? Does ETHZ help with relocation in any sense (even just helping you find a reasonably priced place)? Has anyone been in this position that can offer advice? Much appreciated, in advance.