First, the good news : only one duck is enough for everything. Now the bad news : you'll need to grind A LOT, more precisely you'll need to reach 150 of each for the final badge. I hope you're patient...
Where to start...
Well, once you maximised the dual teagles, you're fine till level 10, because there you need to buy some repair kits or else because of what ? Because of enemies what can shoot you from off screen. Most of the time you just keep aiming the same area, and keep pushing your LMB.
And that's without counting the bugs and fails of the game almost everywhere : if you have 3 weapons, the switch button won't work all the time, a partial repair kit repairs 100 hp not matter how much HP you got, when it clearly says it repairs 10%, the gameplay is boring, some upgrades are buggy as f*** and sometimes don't even display the upgrades. I even paid for an upgraded that INCREASED my reload time.
Next time, put a game that's not in an alpha state, thanks...
Spamming fireballs, confusion and skeletons (maxed of course) make lasting 12 minutes not too difficult honestly.
The sandworm is quite efficient, but isn't that useful later on and cost quite a lot.
With maybe some more balance on mana cost and XP, that'd be just perfect :)
Definitely, 5/5