I've been using FFB wheels in the GT series ever since the first official Logitech wheel for GT3 came out way back in 2002, here are my tips;
1) Set Torque to 4,
no higher, & Sensitivity to 10 (optimal FFB settings for a G29 in GTS). The G29 can't reproduce strong FFB signals, & anything above 4 will make it clip.
2) Put your hands at 9 o'clock & 3 o'clock on the rim, & make sure your thumbs are are in the "thumb holes" on the wheel (
pic). Never change position, & never turn the wheel more than 180 degrees in GTS (till it's upside down &/or your arms are crossed/touching). You'll only need to turn it that far for tight hair pins anyway.
3) Never use the clutch/h shifter for serious racing in GT Sport. The clutch is very poorly modeled & you'll end up getting loads of mis-shifts (afaik it's been deliberately nerfed by PD;
link). Use the paddles instead, & keep the clutch for driving for a laugh only. If you want to feel a proper clutch simulation, then stick to Assetto Corsa!
4) Make sure the d-pad right & left button are mapped to look left & right, this is essential for clean racing imho. Also, have the down button mapped to look back.
5) Give yourself plenty of time to adapt, you'll probably be on pace with your DS4 times in a few weeks/months. When I changed from my DF Pro bolted to a desk to a G25 bolted to a Playseat Evolution, it took me three months until I was comfortable & on the same pace. Sometimes, going from a pad to a wheel can be an even bigger step.
6) Only use cockpit view or bumper cam. The other views are fine when playing with a pad, but, with a wheel it's good to feel you're located near where you'd be in reality.
Enjoy!
👍
PS: As for left foot braking; I always do it when paddle shifting, but when using the clutch I'll mix it up a bit.
PPS: The best training combo in GTS imho is a totally untuned Mazda MX5 on Tsukuba (all assists off/Comfort Tyres only; try mediums & softs). This will help the car to oversteer, & give you a chance to learn car control without any assists kicking in & doing it for you. The car is very predictable, learner friendly, & easy to keep in check.