chriss54002, before I begin to tell you anything, please understand this is my personal feelings and suggestions.
others may have totally different views and comments and none areright or wrong. It's all about what works for you.
Before I began making my own coils, I too used carto's and they worked fine. Making your own coils will give way better all around results.
My first few months of making coils was a hit and miss venture. I made several coils a day and used them at home and relied on cartos all other times. Finally I got a consistent build that was dependable and satisfying, then bye bye cartos.
I don't know what type or style coil built you doing. I suggest to new coil makers to go with a standard size coil via diameter size and ohms. Reason being they are a easier build and faster to make and easier to get consistent. many here love micro coils and that's just fine.
they require a much smaller diameter and many more wraps which can lead to more fussing till the coil is working its best.
so take a easy road till you feel your ready to go in new directions. micros do give a bit more flavor but for myself I like how standard coils work better. It's all personal. I do see here some vapers are returning to old school coils. So I'm not the only one.
It's a must to have a ohm checker, and its nice to have a jig to make coils one. (ex Q vapes coiler)
but a nail or pocket screwdriver works just fine. 2.5 to 3 mm makes a nice coil 5 to 6 wraps with 28g should yield a .9 to 1.2 coil which is fine for most vapers. And is quite safe with most batteries and a stock reos mod.
I do use cotton yarn for my wicks but a wick is a wick and some love cotton and others use other wick material.
If you need any help feel free tosend me a private message