1.Stats: Should Magcargo get a stat boost, Evolution, Mega Evolution or nothing?
In its most basic form, Magcargo is irredeemable. It is one of the worst species in the game and serves no purpose but to hatch eggs, even then Talonflame is better.
Magcargo needs a Fire/Steel evolution. Anything else is simply a distraction. Even though it got +20 BST update in Gen 7, it still has +110 BST to go.
2.Should Magcargo get more abilities?
Desolate Land or even Drought can work. Sand Stream and Sand Force are also options.
3.Should Magcargo get more moves?
Yes. Magcargo needs Power Gem a lot, but outside of that it needs a whole movepool overhaul. Moves like Sludge Bomb, Sludge Wave, Acid Spray, Flash Cannon, Nasty Plot, Shadow Ball etc. can all help.
4.What additional typing Magcargo can have?
Ground, Steel are major options. Bug and Poison are lesser options.