1) Use ONLY authentic Sony, Samsung, or LG, HIGH DRAIN batteries. For a regulated mod, 20A will be best since they have a higher MaH and last longer between charges. Example, Samsung 25R - 20A and 2500 Mah and are a very good battery, (they heat up slower than other batteries), LG HG2 are 20A and 3000Mah and have a slightly longer run time than the Sonys, but the Sonys heat up slower. Don't use any re-branded batteries. You have no idea what is actually under the wrapper.
1b) Amps make no difference at all when using a regulated mod. Regulated mods use an IC controller that sends power to the coil in 2 stages. Stage 1 takes power from the battery and use the amps in the calculation, step 2 uses the volts drawn from stage 1 times resistance to apply power to the coil, so the battery amperes are not even calculated in stage 2. In other words, my 2x 20A LGHG2 can pull just as many watts as 2 30A batteries, but mine last longer since the MaH is much higher.. (3000mah vs 1500mah)
2 Ohm readers are pretty cheap. So it is better to get one and have it rather than not get it and need it. Usually, I calculate my resistance on steam-engine.org and verify on my regulated mod. Since I also use a mechanical mod, I need the ohm reader to check my resistance before I fire the coils, rather than trusting once source, I verify the ohms a 2nd time. This will also tell you if you have a short in the coil, which would be super bad juju on a mechanical mod if you did not test with an ohm reader.
3. Im not sure about other types, but stainless steel will change color when heated. I wouldn't bother with this though, since they are all brown or grey after tuning the coil. (tuning is when you dry fire to make sure the coil heats evenly) When you see "colored" coils in photos, it is because a filter was used and color applied using a photo editor.
