Definitely Rogue is the easiest in terms of gameplay. You get a gold bonus, but Noble is also a good class to start as because you get an XP bonus.
In terms of weapons, the laser pistol (Small Gun 7) is the best weapon, with high fire rate, high damage, high damage percentages to both armor and air, and a relatively low reload rate of 2750 ms. Paired with lvl. 20 reloading, lots of accuracy and armor/air damage upgrades, I find it becomes one of the best weapons in the game.
For buying order, get a house and a henchman as soon as you can. If you don't you will have to hire henchmen and you won't get very much gold that way. Don't upgrade your starting weapon unless you're confortable with how it fires/how fast it fires. If you do like your starting weapon, then go ahead and upgrade. Don't forget to upgrade the weapons of your allies, as they contribute to your overall success.
At the end of each day, unless you are reforging your weapon or getting a new title, have dinner, because this will allow you to level up much quicker. Also, don't forget to get chickens, because they contribute enormously to your income.
The significance of trainers and repairmen is immense. Trainers will also allow you to level up much faster, and repairmen will repair your castle so that there is a chance that you get a perfect game and receive 30% extra mission reward. They also save you in critical moments when you have low health.
There is an option to access mods to the game, some of which are quite handy. You should definitely check the boxes with red asterisks (*) next to them. Another useful mod is the "Bosses always drop MODs" game mod. Since the MODs they drop are almost always more valuable than the weapons they drop, this generates a lot of gold, not to mention the fact that the MODs enhance your gun. Additionally, you get these MODs for free, and do not have to wait until MOD sales day to buy MODs for your gun.
*Whew* That's a long guide, but I hope it helps!
(This strategy certainly helped me!)