1.Stats: Should Galvantula get a stat boost, Evolution, Mega Evolution or nothing?
Galvantula has 473 BST, which is close to 470 and 475 BST, and neither BST has ever gained an evolution. But 475 BST gained several stat boosts and a Mega Evolution, the Mega Manectric. e will discuss each potential case on its own, regardless of their likelihood however, as none of them are impossible.
a.Evolution: Galvantula's BST is not likely for an evolution. Its status a spider Pokémon, which are traditionally two staged, makes this also unlikely. Though its BST is low enough to justify one, its stat distribution is already good enough for a fully evolved Pokémon, sort of, with the combination of its moves and typing.
The biggest justification I can give for an evo is the fact that it has six legs, rather than eight.
b.Stat boost: Galvantula is already the strongest spider Pokémon, so a BST increase in that front is not likely. However Galvantula is one of the stronger Bugs, so a small boost around 10-30 might be possible.
c.Mega Evolution: The closest potential Mega Evolution counterpart would be Mega Manectric. Much like M-Manectric, a M-Galvantula would be good enough and probably expected, but it wouldn't be a primary choice for serious competitive use.
2.Should Galvantula get more abilities?
Probably, as the only serious ability it has is Compoundeyes. Given its dex entry, most obvious ones would be Static and Volt Absorb, but other Electric and Bug abilities can work.
Outside of this, Intimidate would be a nice option, so would Galvanize.
3. Should Galvantula get more moves?
Almost certainly. Bulk of the moves Galvantula gets are physically oriented, even though it is not. What Galvantula needs is a movepool that contains some of the Special moves learned by Ariados, like Psychic and Sludge Bomb.
Other moves like Venom Drench, Shadow Ball and Dark Pulse would be very good as well, but most importantly it needs something to boost its Special Attack, like Nasty Plot.
4.What additional typing Galvantula can have?
Galvantula has a strong connection with Poison and Dark. It doesn't have a strong association with anything else, however.