Go by resistance. 0.8 ohm and above suits nic salts and a tighter draw at low wattage; 0.6 ohm and below wants high-VG liquid and more power for warm, dense vapour. The R and T variants are simply mesh generations of the same idea, and the multi-pack mixes cover both camps.
One to three weeks, in line with other mesh platforms. Prime a new coil with a few drops on the cotton and five minutes standing in a filled pod, keep the wattage inside the printed range, and you will consistently see the longer end.
It fired before the cotton was soaked, and scorched cotton never recovers. Fit the next one, fill, and genuinely wait five minutes; on high-wattage TPP coils give it a couple of low-power puffs first. Skipping the wait is the single most expensive habit in vaping.