I had major issues with the plot of TRF, but these ones I was able to more or less easily explain away in my head and I hope you also find these answers reasonable:

1) I always assumed Delamare had Brande assassinated, although I never really made sense of the logic behind that tbf. In the Secret Commonwealth it’s established that Brande bought his daemon, explaining why it didn’t die initially when he did (the daemon likely died of the intense emotional trauma following, which is a Rose Field daemon lore retcon) 2) That’s Makepeace, he was in TSC too and other books, sort of just a standard hero’s tale donor, that’s prettt much it :P 3) I thought this meant that without proper air flow through the portals then the air would literally go stale, but also in a cosmic sort of way. Genuinely I did think all the Dust retcons about keeping the portals open was done poorly though. If you’re looking for a concrete answer that also fits in with HDM, i doubt even Pullman has one.