Hey.
1. Yes there are some human players, but not very many, I am one of few who plays human frequently. But people play Orcs because Blooodlust is just that much of a game changer compared to any of the human paladins abilities.
2. People do make Sappers/dwarves, it's just they are not seen very often on gow due to everyone wanting to save there lumber to tech to fortress straight away for lust, Players like braviet seem to use them a bit more frequently though, Mages/Death Knights are used always to attack/defend expansions with DND/Blizzard , it's definitely a late game thing you will see, Gryphons/Dragons are ok for some maps but on gow large amounts of them don't end up working well, Death knights and guard towers kill them easy. Though having 1-2 dragons roam the map either scouting expansions or attacking ogres is helpful, but don't
keep them together and overspend on them.
3. Most people play gow, but you'll occasionally see water maps hosted. You will still need ogres to attack the players gold line and destroy buildings, but when it comes to ship vs ship, battleships are good, specially if you can catch some units near shore. Destroyers are good for attacking air units and chasing transports Submarines are good if people aren't paying attention or you're vsing someone newby, but if someone knows where your submarine is, they can just attack ground with the battleship and 1-hit ko it without needing an air unit, tower or submarine of there own to see it.