Since I do this style of trip fairly regularly, I'll answer, even though my experience is in New York, USA:
- Taking a bike on regional/commuter trains on the weekend is usually very fine, so long as it is not a holiday. Which days the train operator considers to be holidays are posted on their website, though not always very easy to find. In New York at least, the full PDF schedule has a few trains marked as off-limits to bikes, and a few marked as especially good (able to carry many bikes).
- Turnstiles are not used for regional rail in New York, though they are for the subway (metro). Where present, the booth attendant can open the handicapped gate for you and your bike--facilities for wheelchairs are generally a boon for cyclists, which leads me to the next point.
- Here, since there are no dedicated bike racks on board, we lay our bikes up in the spots designated for wheelchairs (assuming no wheelchair users are there, of course!). Not every car has such spots, but every train does. We look for the wheelchair symbol on the outside of the train to choose which door to enter. Often there are folding "jump seats" in these areas which cyclists fold up to make room. It is important (even technically required, though not enforced here) to use two small elastic "bungee" cords to secure your bike against against the wall (where there are sometimes small hooks or loops for the purpose).
- No issues with transit employees regarding bicycles in my experience. They've mostly been quite accommodating here.
One additional note: some train operators require a "bicycle permit." My local example is the MTA Metro North system, which charges $5 for a lifetime permit. You can pay after boarding the train, or buy it in advance.
Your mileage may vary quite a lot since we're on opposite sides of the earth, but maybe you or someone else will find this useful. My experience is with the Long Island Rail Road, MTA Metro North, and New Jersey Transit systems.