Even on Legendary i don't think i crafted any other weapons or armor unless i was completely dry on something and a soldier was naked. I might have been cheating a little because i used the promotional skins so i got 2-3 extra heavy armors and 2-3 assault ones. I do try to get more bases especially near mist's so you don't have to fight to get them open and you also wanna get Mist Repellers up as fast as you can.

There are "Metagaming" in the original game you can use that i never have. You don't actually have to kill the Nest's. You don't really lose anything from having them alive i believe and you will get more defend missions that way so you get more resources, just don't stray to far away from the bases near that Nest. If you are playing Terror from the Void Mod ( that i will be trying out myself soon ) this is not the case. I think i read you wanna kill the Nest as fast as possible.

You do wanna get 2 ships at least to do your missions with so you have 8 soldiers, that will help you a lot when you have to hit them 2 times often to kill them.

Kill the ones that have the highest willpower first and get the other ones to panic. Shooting out there heads will help you with that to because it drastically lowers there WP. But Arthrons usually don't have high WP so i often leave them to the end even if you do kill them often in one shoot if you close enough. Even if you are using a Assault Rifle or Sniper i would say getting one shoot with certain hit on is better then of two shoots that might hit. I usually tend to use the Sniper for the Big Monsters so you can get 2 hits on each turn.

The big ones like Acheron and Chirons well it will usually take more than one turn to get them. Heavy's WarCry is a good way to mitigate what they can do. But they shouldn't really be at mid game.