First of all: Hi and Welcome to the FlightGear forum!
Matuchkin wrote in Fri Feb 17, 2017 12:08 am:1. Etiquette: [...] can I just climb into a Cessna 172 and take off on a leisure flight, or should I ask permission to taxi, hold short if prompted, take off at according altitudes and headings when prompted, etc?
Mostly yes, you can just jump in and leisurely fly away.
For a few airports someone will have volunteered to act as an ATC controller on a more or less regular basis. If it is a lot of traffic they might get frustrated when a knew pilot with little knowledge messes up their flow. On the other hand, if there is little traffic they will likely just be happy to help familiarize you with the "phraseology" they use.
While it is not required, some of them announce their planned sessions either in the
Multiplayer events subforum or on the (unofficial)
FlightGear ATC Events website.
In most cases they would rather have you be able to control your airspeed, altitude and heading, than being fully versed in the exact phrases.
It depends. There have been actual controllers jumping in, but from what I hear the level of realism is relatively good. Sometimes there can be downright trolling, intentionally or not.
Usually only the areas around a few airports are controlled; there is rarely or ever any en route control centers.
A note about trolls. It seems the best way to handle them is to ignore them, and for that there is an "Ingore" checkbox in a list of all multiplayer pilots in the vicinity.
Matuchkin wrote in Fri Feb 17, 2017 12:08 am:2. Realism: How realistic is the FDM? How realistic are the planes and all their systems/controls?
That is all up to the aircraft developer. Some aircraft developers have spent literally hundreds of hours tweaking the FDM to meet published performance data and/or flight manuals. Some other aircraft on the other hand are more "arcade like".
Some background may be of help. Currently FlightGear ships with two built FDMs (FDM engines): JSBSim and YASim. One could also plug in an external FDM (for example developed with
Simulink). If a lot of data is known, in particular wind tunnel data, JSBSim is a good choice. Some of the more advanced FDMs therefore uses that. YASim on the other hand is good if only a little data is known (and if the aircraft is subsonic). But it can still do a rather good job.
Regarding systems, there is a few generic systems added to an aircraft that only have a few things configured. Usually there is more than just those and some aircraft developers have like with the FDMs gone to great lengths to make the systems as complete as they can manage (including optional random failures).
Matuchkin wrote in Fri Feb 17, 2017 12:08 am:3. Experience: [...] I play Digital Combat Simulator (DCS), and can fly the SU-25t Frogfoot to its full potential (this means that I can engage ground targets with laser guided, laser riding, rocket, gun and radar/ antiradar guided payloads, start up, take off and land, etc). I can also partially operate DCS's most realistic model, the A-10c. [...] All in all, is this enough experience to even get me
started with FG?
Being able to understand some of the things involved, like checklists, systems and aircraft handling is a good start and will help when trying to understand other aircraft.
Matuchkin wrote in Fri Feb 17, 2017 12:08 am:4. Requirements for installation: I have an ACER Aspire 5250, with AMD Radeon graphics card and AMD dual core processor E-350, along with 6GB of RAM. I am not, as you would call, "computer-smart", so I have a frighteningly small amount of idea on what this all means. [...]
As Parnikkapore mentioned AMD graphics card can have problems sometimes. Most of the developers and many of the users seem to prefer NVIDIA cards.
Matuchkin wrote in Fri Feb 17, 2017 12:08 am:5. What do I need for this? [...] do I need a flight simulator setup (i.e. joysticks, pedals, headphones, etc)?
Some very few actually uses only the keyboard, some other uses keyboard and mouse. Most seem to use a twisting joystick and a few have separate joystick/yoke, throttle/throttle quadrant, and pedals.
Having an axis for rudder control, either through a twist joystick or pedals, make a great difference, in particular in crosswind landings and takeoffs. Flying a helicopter is near impossible without it.
Not game, but flight simulator.
You only need FlightGear and a handful of aircraft of your choice. Some additional programs can be of help, but are not required. For example
TerraMaster, a terrain manager.