Newbie FS 2002/04 question

I am finally getting a decent spec PC from work and want to run
FS2002/04.

I have never played any of the FS games (played Falcon 4.0 a lot a few
years ago).

A few questions

When flying say from London Heathrow to Paris CDG, where does the
aircraft start? At the gate, taxi way, runway??? Do you have to
request engine start and go through start up sequences? If at the
gate do you get a push back? How detailed are the airports -
buildings etc. or do you need the addons for more detail? Basically
I'm asking how realistic is it?

Thanks in advance

Mark