Here is a quick and simple walkthrough that should help you alot.
After the first or second level get the shotgun and upgrade your gold find
Next get enough money to hire a person the cheapest guy will work. The next few levels you should spend all of your money upgrading your helper until he is maxed out on everything. Then upgrade your stats.
Next after you get your stats half way full start upgrading your ammo. I did it in small amounts at a time it works better. After you get your ammo at about 50 buy the next guy, and repeat previous step. The shotgun is very strong and with your upgraded reload you will be fine with the shotgun until you buy and upgrade all of the helpers.
