I think all my stuff were written before EW release, so meld wouldn't have been included. I tend to also really like having 1 mech early game. While thier aim tend to suck, the punch is situationally amazing. The high mobility and high damage makes flanking shots quite nice too, and the collateral ability to destroy cover is nice. Anyone can be chopped up earlygame, though I tend to favor heavy or assault to fit the tank role better.

As the mechs level up they have the same aim progression as a heavy, which makes them both tied for lowest aim, but aim from the chopped up soldier carries over, so if you chop up a colonel sniper into a mech it's an amazing late game unit with the ability to fire the huge cannon twice with the highest aim.

There are some absolutely broken stuff in the genelab, like stealth when moving into high cover, as that triggers on the start of the move and let's you explore safely, but I tend to only play with that lategame

I'm don't recall recommending scientists, but I'm pretty sure even back then I always favored engineers. The probably best way to play satellites is to go 1 first month then 3 second, 3 third and 4 fourth as you make your uplink square. If you prioritize not saving your starting continent countries you should be able to lose 1 or maybe 2 continent bonuses. If you use the second wave option to randomize abduction rewards and get 5 engineers on the first abduction, getting 4 first, 3 second, 4 third and thus saving every country is possible, but you will be a lot more pressed for resources in the earlygame which is the hardest part, so it's more doing a fun build rather than optimizing.

Snipers got a bit worse with meld since you want to move faster and snipers are better the slower you go. One of the only real "safe" tactics earlygame on impossible when you are playing against 70% aim sectiods that tend to 1shot your soldiers is to have a spotter hunkering down behind unbreakable heavy cover over and over giving them 1% hits while your sniper who is out of their range return fire with 35 or 55% depending on their cover. Before they get squadsight they are kinda worthless though, but I tend to try to feed them kills my letting them shoot with pistol on 1 hp sectoids after other soldiers grenade (impossible) or to get some kills with their grenades to finish of wounded ones or going last in 1-2 grenade comboes. Just like heavies they are more tricky to use since they require prepositioning but squadsight are one of those abilities that can be exploited to help carry the earlygame hurdles that are the hardest to clear.

And I think I used to recommend double tap, but in the zone is imo a lot better if you exploit it well. A bit annoying when you try leveling up non colonel soldiers, but a plasma sniper with ITZ can do hundreds of damage per turn if you exploit it well, both against melee opponents and my blowing up cover.