1.Stats: Should Escavalier get a stat boost, Evolution, Mega Evolution or nothing?
End result of a 10-40 sat boost would be similar to Accelgor, it would make it better, though it is already quite good.
The primary problem for Escavalier is however its lack of speed, recovery and priority moves. Only way to balance this would be a hypothetical evolution that forces it out of its shell and makes it fly. However, only male Drilus beetle are capable of flight in the real world, which is an issue.
A Mega Evolution has potential to be powerful, but again, without speed, it won't mean much.
2.Should Escavalier get more abilities?
Battle Armor, Sturdy, No Guard, Sniper, Super Luck, Unnerve and Intimidate are all potentially good abilities.
Clear Body and Long Reach can also potentially be interesting.
Others like Technician, Heatproof and Guts would also be good. Either way, Escavalier doesn't really have good abilities besides Overcoat.
3. Should Escavalier get more moves?
Yes. Escavalier is not lacking in priamary coverage options, but it is lacking in moves in general.
Priority moves like Quick Attack, Sucker Punch, First Impression and regenerating attacks like Slack Off and Leech Life are absolutely essential for Escavalier.
Other moves like Rock, Ground and Steel moves would be well appreciated as well.
4.What additional typing Escavalier can have?
Dark is the primary one, but Fighting also works. The problem is, of course, Escavalier already has a great dual type, which makes this rather pointless beyond a Mega.