1.Stats: Should Gigalith get a stat boost, Evolution, Mega Evolution or nothing?
Gigalith already had a +10 BST boost.
Gigalith cannot evolve further. It can get a side evo or regional form, however.
Gigalith with a Mega would be weird, but useful.
2.Should Gigalith get more abilities?
Gigalith recently got a full set of abilities, so it is not too necessary. Solid Rock or Clear Body would be fun though.
3.Should Gigalith get more moves?
Probably. Gigalith is desperate for a recovery move, maybe Shore Up?
4.What additional typing Gigalith can have?
Ground, Steel and Fighting are the main options.