Okay, so you can't conquer everything on Inferno before Brown shows up. That leaves two options: either don't conquer everything and return to the default difficulty, or come back later. The first option is better because you don't have the upgrade for Pit Fiends and Devils yet – in your case, you do, which means you arrived a bit late. But the key reason is that you're not letting him build up his Pit Fiends and gather a strong army, and you're taking away the enemy's stat-boosting artifacts, which will result in him simply running away in the first round, even with a four-week-old army, only casting Inferno on your stack of Pit Fiends and Lizards, which will resist. In short, Inferno becomes a pushover.
I didn't understand the point about Green's first appearance. In my case, he showed up as a day-one hero on the second month, got beaten, and didn't reappear until weeks 41-42. I was just returning after conquering the Citadel lands and, in principle, easily defeated Lork with 220 Scorpians. And Green started showing up either very weak or with a week-old army. He never showed up for the Red-Blue computer respawns, only if he was extremely weak with just 1 Harpy.
Brown is the problem. But only because this jerk doesn't show up until Tazar is nearby. And I also feel bad about the Passives at the teleport, I haven't leveled up all the weak heroes on them yet. On 511, there are only two heroes with experience in Passive fighting and Logistics. And you can also level up weak heroes with resistance, which will be the least painful way to deal with Inferno computers.
Regarding Inferno garrisons, by the way, I postponed them until weeks 44-51 – there, Pit Fiends were one-shot by snakes with Bless, and the losses were quite small in the end – only 100 Lizards and Pit Fiends in total. I don't really like the idea of losing main stacks if it doesn't lead to an increase or decrease in losses in the future.
Regarding the program – I don't know, I haven't used it.
Yes, the Magma Elementals stat event is very well hidden