There are multiple places in which guilds can grind their "Guild EXP". This is seperate and different from your regular EXP. One kill can be appoximatly 2-3 EXP (From personal experiance on regular mobs). As you've realised there is a damn lot of EXP you need to gain to level up. 64k aprox for level 2, 360k for level 3 and over 1mill for leve4, so on so on. These grant buffs for all your guild members.

Level 1 = +10% HP and Mana and 30 to all stats.
Level 2 = +5% HP and Mana
Level 3 = +5% Increased walking and mount speed
Level 4 = +10% Drop Rate
Level 5 = +3% Attack, Defense and resistance in PVP
Level 6 = +5% Phy/Magic attack, phy crit rate, magic crit rate.

Good locations to grind these EXP is the "Utran Platform" in the "Sea of Hakanas"
Crewmen = 3xp Per kill
Skanners = 2xp Per kill

Another location to grind is the "Cemetery" in Hakanas Highlands
Skelebobs = 3xp
Zawmbies = 3xp