Ok so I played this game with a lot of melee, and I mean a lot, heck I was able to beat the first boss with melee only. Melee in this game is extremely good, though the first few weapons were fairly jank, they have better damage than the guns you have. Also the zombie AI in this game is fairly broken, they can't determine Y axis at all when attacking. Here is a fairly good cheese for anyone having trouble early on, find a stair case, then lure the zombies chasing you up the stair case. Instead of getting on to the next floor, press down on the stair case ONLY WHEN the zombie chasing you is also on the stair case. You will phase through the staircase. The zombies will be locking on to you, but they won't come and get you downstairs. Simply move to the start of the stairs, they will follow you, judge the distance so that you can hit them, but they can't hit you. This works for all zombies in the starting area, even the guards zombies AFTER their charge attack.
You should also know that there are no auto saves, you will always respawn at saves point, also zombies respawn when you reload a saves, so if you find a good area you can start farming zombies there.
There are three very good farming area for currencies in the game. The location of the first save point. Where the huge naked girl background was. In this area there's a lot of zombies, but there's a huge stair system, proceed with stair cheese to farm. On the left of the room, there's a door, proceed through that door, and then continue to the end of the corridor and proceed through that door. In the next room, when the music started playing, rushed to the stationary turret and blast away, if they overwhelm you rush to the door you just came out of and enter again to reset zombie location.
The second location that's good to farm is the sewers, the bugs drops decent gems, but the cream de la cream are the fat zombies. They only drop 3 gems, but each gems gives 10 currencies, making them the most gem drop enemies in game beside bosses.
The third good place to farm is inside the bandit base, all saves point in the bandit base is good farming. Though WARNING: There's a hard cap on ammo in the game, since enemies DOES NOT drop ammo, they only drop grenades and health, and all stores in game have ammo cap AND THEY DO NOT REPLENISH. So farm at bandit base if you are confident in your ammo reserve or your melee skills.
Finally there are some enemies that have 2 defeated CGs, meaning you have to get defeated by them twice to get all the CGs, though if you are lazy, you can just skip these duplicate CGs since they only add more zombies into the CGs, the defeated pose is the same.