I went ahead and moved this into the 450 section. It's amazing that you have "uncrashed" heli's lol. That is a rarity on here. As for the setup, the first thing you will want to do is have good electronics. I'm guessing with your trex, you have the 410 cyclics and either the 420 or 520 tail servo with a 790 gyro. If so, you are set. I would set everything up according to the instruction book as Align has great instructions and you get your heli very close if not perfect on the first shot.
Because you are wanting to fly scale, I'm sure you will not want to fly with a flybared helicopter. Going with a flybarless head will add an even more realistic look to your scale bird be it with a 2, 4, or 5 blade heli. When you go flybarless, you will need a 3 axis gyro, and the 3GX is a great system offered by align. There is also one that Lee has purchased. It's the 3 axis gyro and a DSMX Rx built into one. Great performance as well. The upside to this is you have one less item on your heli. I want to say it's called the BeastX, but I will let him answer that one.
Going FBL will allow you to have a much more stable, yet responsive helicopter. Since the gyro will be helping you, it should make flying a little easier. the one issue that I think you will have is with the bodies with retracts. Those require an extra channel, and the one that you need, the gyro plugs into. Now, if you want to run your gyro in Rate Mode for the ultimate scale look, then you can unplug channel 5 and plug your retracts in there. Rate mode will only stop the movement of the tail, but it will not return the tail to the "heading" it was facing before it was moved. Most scale guys that I have talked to fly in rate mode because of the way it looks. You will have more of a weather vein effect than you will with a HH gyro. And sideways flight will require lots of rudder input.
As for dual rate and expo, this is a new territory for me. Fiberglass bodies are heavier than these heli's were made for, so you will have to play with your pitch and throttle curves. however, if I was starting out with this setup, here is what I would do. I know you are not wanting to do anything in idle up or 3D, but you need to setup the head in idle up. This way, you can know for a fact that mid stick is at 50% and 0 degrees of pitch. Full stick should be around 12 degrees (I usually say 11, but we are dealing with a heavier bird here). and you need negative 12 as well. My videos explain in detail how to achieve this setting, but I will post it here if you need more help.
Now unlike my videos, on a scale heli I would suggest that you fly only in idle up or have a very flat throttle curve. This will keep it more realistic. I would set it up where you have 80% power, or even 70% power at all times, but keep your pitch settings around 45, 47.5, 50, 75, 100. This will allow you to spool the heli up on the ground and give you just enough negative pitch to keep you on the ground.
Dual rates. I would set the high rates just as the book describes, then set low rate to 70% and try it. If low rate is still too twitchy, then lower it to 60 and so on. do this until you like how it feels.
Expo is something that not everyone likes, but I love. I have just started flying my planes (Edge and Extra) on full rates all the time. And the only way to do a smooth takeoff and landing (my landings still suck lmao) is to have very slow servo movements at the beginning travels of stick movement. This allows for a more precice movement and when you are talking scale, that is what you are looking for. I would start off on 45% expo on high rates and 35% on low rates to start with. Fly it and see how you like it. If it's still too twitchy (and I'm sure you are not a stick banger unless you mean to), then raise the expo.
I hope this helps. If there is something that I have missed, let me know and I will cover it.
Also, welcome to the forum, I hope to see some flight vids very soon. yes, I want to see your planes as well lol.