Try to classify your game maps into 3 Regions - Town, Story and Dungeon. Town can be resting area and shopping. Story map can be side quests and Game lore. Dungeons would be the final aspect and a boss fight. It would suffice to have just these three maps since its your first game.
Personally, i use a formula like a.atk * 0.5 - b.def * 0.25
This kind of a damage leaves very little room for errors or imbalance. Just be sure to allocate enemies 30 to 50 % less stats than player and you should be good. Use multiples of 5 or 10 for armor and weapon stats.
Stat Example :
Early Game :
Player would have 45 atk, 25 def, 75 health.
Enemy would have 25 atk, 10 def, 25 health.
Late Game :
Player would have 145 atk, 75 def, 215 health.
Enemy would have 115 atk, 45 def, 150 health.
Gear Examples :
Rank 1 Weapon - 10 atk, Rank 3 Weapon - 70 atk
Rank 1 Armor - 5 def, Rank 3 Armor - 35 def
Most of your imbalance comes from levelling stats so minimize the stat gain per level and you notice things being pretty balanced. You can modify stat gain per level at a later point in the game if needed. Keep the stat gain per level for Health the same though, thats needed while balance testing.