devtrackers.gg
Edit circle settings, yes. You can even have it so it doesn't move in until after an hour, so it doesn't affect anything. You can kinda go wild there.
Vehicle spawns, you can't increase. The way I tend to do it and I see it work for others, is run it in esports mode (so you get hard spawns as well as random spawns) and give Zone 1 a 10-minute timer or so, this will let everyone find vehicles and get to the start point. Then the race starts once that timer ends. Then have Zone 2 to not decrease very much (honestly, it takes a bit of time to learn the bluezone settings so get testing!) so it doesn't affect your route :)
...
...