As far as
when? No one knows.
I don't think anyone was expecting Red Bull Ring this month, track predictions are really hard to lay down, maybe aside from Le Mans. I do think it's likely that real world tracks that were new or updated in GT6 have a higher probability of returning in GTS - at launch we already had Nurburgring (updated seemingly every time PD get's a chance), Brands Hatch, Willow Springs, Mount Panorama (Bathurst), and Suzuka (updated in 2014), and then post launch we've recieved Red Bull (also post-launch in GT6), Le Mans (had updated time night time sky boxes), and Monza (don't recall if it was ever "updated", but an "'80s variant" was added with the Senna content). Tsukuba may be the outlier here, as I don't believe it had any touching up in GT6. Regardless, I'd lean towards Silverstone, Spa (added night ToD in GT6), Daytona (added night ToD in GT6), and Ascari being the likely eventual returning faces in GTS. I'd put bets on Laguna Seca as well simply due to it's heritage to the GT series, in fact in that regard it falls in a similar place to Tsukuba.
Interestingly we could see Catalunya as early as this month - peep this article:
https://www.gtplanet.net/gt-sport-24h-race-catalunya-announced-track-coming-game/
There's supposed to be an esports event at the venue at the same time as a 24hr event on the circuit, very similar to the Nurburgring event back in May. However, that doesn't necessarily mean the track is coming, they could use other tracks for the races - they didn't only use Nurburgring in May.
Despite Spa clearly being the most popular fan request, I don't feel like it'll be the next real world circuit to arrive (talking beyond my Catalunya prediction), I think Silverstone may be next. It's much more of a hunch than anything honestly, but I do think PD will have better connections (GT Academy comes to mind) and easier access to it than most other circuits not yet in the game. Ranking by likelihood I'd actually put it Silverstone-Laguna-Spa-Daytona.
Those cars? We've seen quite a few new-to-the-franchise "modern" cars added since launch (though it depends on where you make the cutoff for "modern"), but I don't think any of them have been a top-of-the-line super or hyper car. Of your list I think the Chaparral is most likely, but I'll save my whole car prediction spiel for a more appropriate thread.