The quality varies but it sounds like you've done your research. A good person to my understanding won't go that deep. If they need to keep applying numbing cream it's not a good sign. I don't think you need to apply numbing cream before, the technician will apply some during the appointment. Definitely follow advice around alcohol/caffeine etc beforehand. It definitely increases potential for bleeding which makes the process harder and less successful in terms of the due sticking. You should have all this in the instructions before you go.
I've had mine done three time by two different people. The first one was too far off my natural shape and too deep plus the dye faded out to a pale orange colour. Second person much better more modern technique, not as deep, closer to natural shape and filled in/slightly adjusted rather than totally changing shape. Fading out to lighter brown.
You can go as thick or thin as you like. I think a combination of powder and blading is good as it's more likely to last than micro blading alone (which usually loses definition anyway over time into more of a powder brow look anyway). Especially so on oilier skin. MB lasts better on dry skin.
If you have oily/combo skin it may fade quicker and you need to be even more scrupulous with after care.
You will have comedy angry bird eyebrows for about a week no matter what. Do not panic and avoid any important social events. Most people these days will straight away realise you've had your brows done.
With aftercare, absolutely do not get them wet, do not pick at anything even if you've got a whole flake of skin hanging off (they will most likely flake after a few days - gross but part of it). Quite literally do not touch them, don't put creams on them etc until the end of the healing period. If you do, you'll risk pulling the dye off those sections and end up with gaps.
Most places you would have a touch up after a few weeks so you can always go slightly darker, fill in gaps etc. Follow the advice given by the person doing it word for word.
It sounds faffy and complicated but honestly it's worth it for a week of ick. It's a totally game changer for most people that makes you feel better with actual eyebrows and saves time not needing to do them every day.