1.Stats: Should Wailord get a stat boost, Evolution, Mega Evolution or nothing?
100 BST gap is what Wailord has, which would argue for a pre-evolution to Wailmer. If this is not attainable, at maximum +40 BST can be granted.
An evolution would have to work similar to Porygon-Z, with completely new stat distribution.
A Mega is the same. Since Wailord has massive HP, anything else can be buffed, but a redistribution of stats would help better.
2.Should Wailord get more abilities?
All abilities Wailord has are terrible. Better options would be Drizzle, Swift Swim and Thick Fat.
3.Should Wailord get more moves?
Wailord's moveset is terrible. Most missing move for Wailord is Slack Off, but outside of that, moves like Rock Slide, Stone Edge, Earth Power, Calm Mind, Stockpile, Swallow, Spit Up, Weather Ball, Aqua Jet etc.
4.What additional typing Wailord can have?
Normal and Ice are the most obvious ones. Psychic, Ground, Rock and Steel would be lesser options.