1. what happens to normal terrestrial channels (bbc1, bbc2 etc). do you stream these instead of having an aerial?
You can freely stream non-BBC stuff where available (4OD etc..) BBC player requires a license fee to be paid though.
Some (a few) BBC dramas are on Netflix.
2. can you get channels like ukgold, dave, discovery etc, or do you lose these?
AFAIK none of those channels offers a streaming service.
3. is the complete film library free on netflix when you subscribe? does any stuff cost extra?
no additional fees on Netflix - just chose your subscription level based on mobile devices, SD, or HD etc..
Amazon does offer additional channels via third party providers that you can pay extra to watch.
Also Amazon video (separate to Amazon prime streaming service) has newer releases of movies you can rent etc..
4. what hardware do you need? if a smart tv has the netflix app built in, is this sufficient or do you need an extra firestick type device?
if a smart TV has Netflix app built in then you can watch Netflix...
likewise ditto to prime, iplayer etc.. (though remember you need a license for iplayer so might as well make use of Freeview/freesat too if you do buy one)
5. is firestick, fire tv, and netflix the same thing?
no, firestick is piece of hardware from amazon that allows a non smart TV to watch amazon prime, Netflix is a streaming service available on multiple devices.
6. what resolution content do you get compared to virgin tv?
That depends on what you're comparing it with... if you only have an SD subscription to Netflix then you'll only get SD content... etc..
Anything else ive missed about switching away from virgin media?
Sports etc..? Though amazon has some.