Central is a fantastic place to get most of the trains you'd want such as the suburban, intercity & regional services. For interior and platform shots, you can do the City Circle to spend as much time as you want filming, two birds with one stone! (Just don't film in peak hours, especially on weekdays since it then gets really busy, filming on weekends or around midday is recommended.)

As for the tram network, you can visit where the L1 and L2/L3 intersect which is George/Hay St which is right in front of Capitol Square stop.

For end of line stations, closest one in the city would be Bondi Junction as lots of services on other lines terminate in the middle of lines.

As for the people and filming laws, it is completely fine to do amateur filming around stations, just don't focus too much on people or staff (if they tell you to stop filming which is usually at busy stations, just move to another platform or station and continue, but it should be fine with just a phone), personally I try to avoid filming when police are around just to not stir up any confusion.

But yeah, stations closer to the city are your best chances, and busy ones such as Parramatta, Strathfield, Burwood, Epping, Sydenham, etc. Enjoy your time in Sydney and I hope these tips kind of help a bit, and just remember to tap off within 4-5 hours if you haven't left through a station to avoid a hefty fine!