Why do the fights tend to give more focus to Oarai's opponents? Because they've already proved themselves at this point, they're no longer the underdogs from the TV series (and the movie) and are even considered The Dreaded. Meanwhile, some of the opponents they've faced so far have their own issues and can even be considered to be underdogs in their matches.
This appears to be a deliberate design; when Saunders girls are discussing the tournament, they claim that the tournament is revenge match of the favorite schools, i.e Oarai's opponents in the Nationals. But if you see the tournament bracket, you'll notice that everyone of those opponents, except of Saunders and they still need to contend with Jatkosota who are The Dreaded in a different way, are in the Group B. Which means the 'revenge match' won't happen until at least semifinals as the favorites would need to elbow each other out of the tournament first to get to Oarai, giving the less prominent schools to test their mettle against the National champion.
Why does BC Freedom's Marie use an outdated Renault FT? Precisely, because it is an outdated tank that can't really stand up to any sort of bombardment. Episode 2 shows that, for it to survive, both sides of her team (the Escalator and Examination students) will have to work together if they hope to survive.
The lake seems like such a bad place for Oarai to wait for Chihatan since it leaves them out in the open compared to the jungle. And that's before we learn that the latter has amphibious tanks. However, it also means that there's only one direction from which Chihatan can attack. Miho most likely chose that part of the lake since there was a direct line from it to the sinkhole they found earlier, meaning that she could easily goad Chihatan into chasing them towards it.
In Episode 4, Alice makes an appearance as a transfer to St Gloriana, still in her Centurion. Though a distinctly post-war tank, it's still of British design and manufacture, thus fitting in with her new school, and it succeeded the various then in-service tanks, which can be interpreted as Alice's succeeding Darjeeling as St Gloriana's field commander.
