A Wotofo Sapor is a good choice for a starter in an authentic that won't break the bank. It's extremely flexible and can be built either for flavor or cloud. It's also top-air, which is helpful because all new drippers, and not a few experienced hands, tend to over drip from time to time and top air helps prevent it from puking juice all over your mod. There are other choices, of course, and a number of good quality clones available for $10 and up. Resistance of the coils, on a regulated mod, is not as important as it is on a mechanical mod so long as it falls within the ability of the mod to fire it. What controls battery draw, and thus safety, is the watts you set, versus the voltage the battery provides. For maximum safety, and using a good quality 20A battery, stay under 60 watts and don't worry about resistance too much; the mod handles all that for you. However, there are serious safety considerations in coil building as a short can be a real problem. Theoretically, the mod is supposed to catch that, but I don't like trusting them myself. I do recommend the purchase of an ohmmeter. You can get cheap ones for $15 on eBay, and top of the line from USAOhmmeters; their "Ultimate" model is the one I use and it's $27+ship. A separate ohmmeter will help you make sure you don't have a dead short before putting it on the mod at all, serves as a handy building stand, and is useful as a check on the mod's ohmmeter and is usually more accurate.