Merlin Mini wicks a bit differently then the Merlin, it does not need as much material. I do big bushy floating wick on the Merlin, Mini seems to prefer less, and in the cup wicking.
As for coil size, my suggestion is if you run the airflow pretty tight try a 2.5 mm, if your more open on the airflow run a 3, or even 3.5, I run my airflow wide open, and get noticeably better flavor with a 3mm over 2.5 mm, 3.5 changed the flavor slightly, and depending on
juice can be better. The 3.5 seems to bring a little brighter flavor to fruits, but suffers slightly with bakery/desserts. I've run a 2.5 in mine, and with open airflow it did not produce flavor as well as the larger, but with a tighter airflow it did much better.
Since I like open air I stick with a 3mm most of the time, and is probably the most versatile build for me.