Long post, but maybe helpful if anybody is thinking similar/if this appears in anybody's feed:
I remembered this thread from ages ago and yesterday, 15 months later, I finally did it and attended a proper track day at Bedford (I did go to Blyton Park last summer but it was a private day and only 2 cars on track at a time). I managed to find a novices day so a good place to learn with less pressure, though there were still some quick cars around who were probably not the same definition of novice as me.
Unfortunately there were no instructor slots left even when I booked it months ago but I saw it as a chance to learn how everything works on a track day and try to at least keep to good lines through the corners. The day was run by MSV and was super smooth, everything was on time and well organised. The entire first session was following laps, but the pace was pretty good and I really appreciated 4 laps in a row with no worries about overtaking.
Reading back through my posts above, one of the worries I had was traffic. During the second session (i.e. first where you could overtake/drive for yourself) I had to overtake a couple of cars myself and also let faster cars through which was good to tick off early on and wasn't really an issue. This could've been because everybody there was pretty decent and respectful too. One thing I did find tricky was when you got caught in a chain of cars. I only really overtook on the main straight and the one parallel to the the start/finish (towards the end of the lap) as I didn't like risking anything too close to a corner on the shorter straights such as the pit straight. However, if there were 3 or 4 cars in front, it was tricky to leapfrog them so I did have the odd lap in a big queue and then waited to pass as things opened up / those in front overtook one by one (screenshot below from random YouTube video I found, it took me another lap to get through). If a faster car appeared though then this got difficult as I tended to pull over pretty early on just to get them out of the way. This meant that I sometimes missed the chance to overtake myself, but I suppose it is better safe than sorry.
Again as per the above, the first hairpin wasn't too bad at all and the corner into the pit straight was one of my favourites when you got it right. The car was also great in the S bends after the hairpin. It held its line really well on the sweeping bends too and it was fun to be able to push it, which I suppose you only get to ever really do on a track. I did notice the body roll a fair bit, but it never felt out of control and I guess that is the style of the car.
While it was a superb day out, at the moment I am a little in awe of how much there is to take in and build on when driving quickly on a track. Part of me wonders if it would be good to have a slower car too so that you don't get away with mistakes (with the Yaris you can still get out of trouble if you are slightly on the wrong line), but then again that's the fun of owning the car and may as well make the most of it.
Technique wise I noticed that I tend to brake quite hard when coming right off the power into corners (i.e. so that the hazards trigger). I'm not quite sure how good this approach is vs coasting a little yet less braking and carrying more speed. Sometimes I'd also start turning too early and not doing one thing at a time. I found that I preferred the slower more complex corners, but the scary bit was the chicanes or hairpins after the long straights where you were flat out (i.e. where to pick the braking point, how much speed you could carry, and when to trust that you would make it through). I like to think my lines were ok-ish (and had watched various onboard videos for tips beforehand) but without an instructor, its hard to tell. I was far from the fastest but the car did let me keep up with others in the twister sections. Still, plenty time to learn and there is zero need for me to invest in any performance upgrades that's for sure, as I am by far the limiting factor though I may get some braided brake lines. I'd love to see what a lap is like when the car is in the right hands.
In a way I was glad when the final session was done and there'd been no issues at all during the day, but equally sad as it was a brilliant experience. I was amazed at how knackered I was (albeit there was also a 2.5 h drive back home); think I'd driven >100 miles on the track over the day (helped by it being a long track at 4 odd miles). The day was in sessions and the concentration required made me grateful that each was only 20 minutes, if it had been open pit lane then I might've over done it.
Over the day I also managed to use most of a tank of fuel so was glad I filled up the night before. There were zero mechanical issues as you'd expect, I even managed to take the tow hook cover off no problem (definitely use trim tools as others previously posted), may need new brake pads soon though and the tyre wear was noticeable by the end of the day. I took some air out in the morning and during the laps, the pressures had risen to bang on what they should be at normal temperatures, so that was a lucky guesstimate.
The obvious next step is to do another couple of track days and try to get an instructor (as per the above, this might be another stressor but worth it in the long run). I'm thinking I might stick with Bedford or try to find a day at Anglesey for a bit of variation and a shorter track (on the straights I did sometimes struggle to overtake cars I'd caught in the corners). The reason being that both have plenty run off areas and are nice tracks for learning on. My local track is Castle Coombe but I noticed that some track insurance quotes ask it's one of the tracks you will be planning to visit (grouped with the Nurburgring), so I guess its reputation isn't unfounded. I'd love to do some of the classic 'proper' circuits e.g. Brands Hatch, Oulton Park and Cadwell Park but I think sorting out the overtaking and being generally more confident especially around traffic needs to come first so I might do a couple more of the wider tracks. At the rate I am going though, it might be several years though as when you added in fuel and hotels it was a fairly expensive day. I suppose doing more and more lets you build on things before the skills fade.
In summary, it was well worth it and the car is great - so glad I finally booked it and gave it a try. Probably one of the best experiences I've had in my car, and more generally in life (honest). If you are considering too then it's well worth it. I love driving on twisty roads but what could be around the next corner is always at the back of my mind. As such I drive quite conservatively. Going onto the track opened up a whole new aspect that you just can't get on the roads and a whole new puzzle to learn. It was fun to push the car a little more towards what it is meant to be doing. Bonus pic of an amazing looking NSX: