Everything you felt and are expressing here is normal... just keep that in mind. We for the most part are all risk adverse in that none of us want to damage our cars, selves, and/or others and not uncommon to be in the back of your mind out there. Coming in with a bit of caution is healthy especially as you start out. In time though the trick is getting your skills - and just as important - your confidence in those skills - to a high enough level that you are able to maintain a good pace and enjoy your time on track. Good thing with tracking is that the learning curve is very much exponential and explodes at the beginning and then flattens out as you progress.
You mention brake fade being a big cause of uncertainty while you were out there. My belief is that braking sets the foundation for good pace. Without good, consistent braking you cannot set a proper braking point and this will lead to inconsistent entries leading to inconsistent exits. Plus if they do fade that can really, really suck - really, really fast. You said you are on stock pads so I'm assuming stock fluid as well - these are both insufficient for track work. The M2C is a big, heavy car that is easily capable of overrunning the stock setup on a track. And you don't have to be a pro that is threshold braking every corner to do so. Novices can actually often be harder on brakes and introduce fade long before a pro would even running a much higher pace on the same car. Dragging out the braking zone is one way to increase the heat in the system. Running DSC or MDM and tripping system uses the brakes for the correction (and yes the fronts too) which can also add more heat. At minimum I would recommend a good track pad and an appropriate fluid. I really like Castrol SRF for dual usage cars due to the minimal fuss combined with excellent performance. Pads there are multiple good options out there. The main takeaway here is that even though you are new do not underestimate your ability to fade the oem brake setup. Even though you are somewhat high risk tolerance I would still invest some money here to help avoid this.
Body roll, spinning out - you are going to get body roll with the spring rates the M2 comes. The trick is to get comfortable with that feeling. Keep in mind that the car will communicate with you before it wants to break loose though. With the 4S you are going to hear them start howling - and when they do know that they are approaching the limit (approaching is the key). I do not like audible ques because as you get faster you might find that sound is too slow to respond to but at the beginning it can be very helpful. Getting comfortable at the limit of grip is what tracking is all about in the end and another good way of doing this is going to a car control clinic/skidpad time/etc. We are not born with the skills to make these corrections - we have to build them and then ingrain them to the point that they are a reaction. Spending some time in these situations sets this foundation for you and can really spike that learning curve. If you are not comfortable saving the car if/when you go over the edge it is very, very hard to try to find where that edge is. I'm not saying you have to be pushing 10/10ths on a track but still having - and knowing you have - the ability to control the car is extremely important. Also it is much easier to build this skill set at lower speeds so doing it early and when the car is at its slowest is a very big help. Also spinning out is not the end of world (unless it is) - as long as there is no harm done just keep plugging away at it. Doesn't mean go spin out all over the track but yes it does happen. Sometimes getting that first spin out of the way can be helpful
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For new track drivers I really like to stress lets focus on your situational awareness. Once you are 100% comfortable in being able to pick up all the flag stations, knowing where all the cars around you are, and then being comfortable around said cars - time to start picking up the pace. First thing first - make sure you are safe for yourself and others. Know at all times if the track workers are trying to communicate with you. Know where all the cars are around you. Don't drive out of your mirrors if someone is behind you. Don't get target fixation on the car in front of you and follow them off when they are driving out of their mirrors watching you and miss the corner. Get this awareness down, get comfortable, apply speed.
Motion sickness - hopefully that goes away completely for you. I get it if I'm a passenger but as a driver the only time I will get it is during prep work on out laps. If I'm in a competition and have to prep the tires and brakes with lots of stoppies my stomach will absolutely hate me by the end of the out lap. Otherwise once I get going all is fine. Since you saw improvement throughout the day hopefully it progresses and goes away.
In car video with a bit of data overlay can really help too. Seeing your inputs lets you know what you did - good and/or bad. Also lets you get the viewpoints of others that can help (just be careful who the "others" are). Coaching is an excellent help again if the coach is qualified. And like you said seat time rules all. Proper practice is the key.