4/5 often not express on weekends. If you don't make the connection, it's 20 mins between PATH trains. 20 mins to from WTC Harrison is also optimistic (33 mins per the schedule, often longer with a wait at JSQ).
Nonsense. You can take the 4 or 5 (Lexington Avenue Express) to Fulton St. station, which takes 20 minutes, then walk a couple of short blocks to WTC & take the PATH direct to Harrison, another 20 minutes.
45 minutes total, if you make the connection.
From GC, 45 mins is wishful thinking, an hour is possible if you're lucky, but you can easily hit 1.5 hrs or more. I'd say the median would be close to option 3.