I wouldn't say I'm an expert (especially as I've never owned a genuine one) but I do have a few and use them very regularly.
1.8 coils and 12mg Manabush is exactly what I vape.
The grub screw is the airflow control, if you like it wide open then I suppose it doesn't matter, I usually adjust mine in until there is just a little resistance on the airflow ...
The tank is bottom fill, it looks like you could fill it by unscrewing the top (like you would on a Nautilus 2) but is it 100% not advisable and will lead to all manner of heartache.
when you fill don't go right to the top of the chimney spout, it's impossible to fill the tank to the brim, so it will always look like it's only 3/4 full after you've filled it ... once you have the liquid in the tank make sure the coil is tight in the base then drop it down to meet the threads in the chimney turn the bottom of the tank (the bit with the coil in) in a reverse direction until it 'clicks' and kind of drops down a little into the threads, then proceed to tighten the coil into the chimney in the clockwise direction ... this should make sure the threads don't get crossed or jammed in the chimney. There will be some resistance from the o-ring (make sure that has a bit of liquid on it (or on the glass) but it shouldn't be too hard to turn, if it is then something is not threaded properly, also make sure the coil is sat in the base straight (you can see this by eye before screwing it in) if the o-ring under the coil isn't sat right or (as I've had once before) the coil threads are badly machined then it won't be straight and then when you try to tighten it into the tank it will be pulling at an angle... but this is very rare for that to happen.
It's basically the same process as using the original nautilus which I was using before so it wasn't new to me when I got them but still now I find them very easy to deal with and hassle free.
I can only speak for the clones I have (these ones)
https://www.fasttech.com/p/3870800
but I bought the first one June 2016 and it's still going strong, there are some other Kabuki's on FT that are total garbage (I bought one and chucked it in the bin when it arrived) so if you have one of the bad ones it may not be workable if it has threads as bad as the one I have.
I'm out this evening but if you need any more help or want to ask more questions, I'll get back to you.