JoshC.'s post in Fright nights annual pass night was marked as the answer
Last year's event was very reasonable - don't remember queueing much more than 10-15 minutes for any maze or ride really! Pretty certain got a few re-rides too.
Other events are harder to compare to since they were either shared with media night (making them a bit busier) or very limited. However the atmosphere is usually very relaxed in the sense that it's easy enough to get everything of note done without rushing.
JoshC.'s post in Does anyone know if summer nights for AP is going ahead? was marked as the answer
Summer Nights is not scheduled to happen this year.
JoshC.'s post in Annual Pass Guaranteed Entry was marked as the answer
There's no way for AP holders to guarantee entry outside of FN.
Probably your beat bet is to just arrive at like 9am. That way you get in the park when it opens (and is at its quietest), and you avoid running the risk of a capacity park.
JoshC.'s post in Buses to thorpe in closed season. was marked as the answer
There are still buses, but not the Thorpe Park Express (for obvious reasons).
You can either get the 446 or the 51 from Bus Stop 2 at the bus station.
I think these are the most up to date timetables for them:
446 - http://www.surreycc.gov.uk/?a=357416
51 - http://www.surreycc.gov.uk/?a=173424