Yes, 2.4 Ohm carts at 3.7 Volts is definitely the way to start. 5 Ohms is for power users, like the dual top. Hercules is even harder to master, I would not try it until you have Omicron with carts sorted out.
Yes, running them dry at 7.4 Ohms is wrong.....which is why the instructions tell you not to do it. It can very quickly wreck the cart, most likely by making it leak costing you .2 grams or so of concentrate....plus the leak. The universal advice from experienced owners seems to be 'don't do dry burns' (including 'oxidizing') at all. It's come up several times, nobody seems to defend the practice.....lots of guys have had troubles. Sometimes otherwise good carts are far enough off center to not show the glow anyway.
Get some 2.4 Ohm carts, load them carefully (watch the preheat of the center section, most important) and not loading more than .5 at a time and you should be on the road.
Good luck.
OF