Hi Leo,
I'll try and answer a couple of questions...
First off - drill
elder drill is good. I tend to work on a drill the thickness of my little finger tip to the thickness of its base, so 10-15mm-ish diameter? I have tried finer drill but have not got very far with them - a bit too flexy for me and not enough sidewall to pith. Give different things a go though - not everyone works the same.
cut green elder, carefully debark it and set to dry. Elder from 2nd year growth is best because of the thicker side walls - you want maybe 50% pith for a good drill. the less pith the more side wall, the more friction surface. Shade-grown elder often grows thicker walls as it is not putting on as much height. You want a seasoned (dried) drill. If elder is dead already it tends to have rotted a little and softened and so doesn't have hardness to be an effective drill. Hand drill tends to need a harder drill than hearth.
You want to trim any bumps off - bumps cause blisters. Kinks are a problem too - blisters and they stop efficient drilling. When drying you can lash a kinked drill to something straight and rigid so that it sets straight and/or use direct heat to make the wood more elastic, bend to straight and let it cool.
Hearth.
twice drill diameter is fine, flatten so that it lays nicely on the ground. Clematis is great, ivy too. Like bow drilling, you don't want rotten-soft wood - it just falls apart too easilly without charring. You do want seasoned wood i.e. dry - dead standing is great (pre seasoned) but dead and punky is useless, you will just drill through it. Fibrous and sound wood like clematis and ivy is good. Standard hearth boards of lime, willow and sycamore also work well.
Drilling
start the set like bow drill - burn-in a hole and carve a notch. I've found with pithy drills (elder) that a deep notch that actually cuts the centre of the depression is best otherwise a peg develops in the centre and wears away the pith whilst slowing drilling. Standard 1/8 circumference is good for notch width.
I would expect you to get smoke on your first attempt, but thats a long way from an ember. best thing is to learn to relax into it, get a feel for speed versus pressure. More pressure can be gained from using the sides of your hands more (the edge down from your little fingers). I tend to get more speed from the flats of my hands. Excessive pressure = blisters.
Start like a bow drill, get a rhythm, let the set heat up a little, watch for smoke and char. Next pick up speed whilst maintaining pressure. You will have to work out for yourself this bit - hard to describe.
I've seen you have got a couple of people recommending thumb loops. Not tried them myself, but you won't be teaching yourself proper pressure transfer that way, and you are adding another component.
As for a reliable choice for fire starting. You will get a smaller ember - so tinder is more critical. Humidity is a big problem as is water content of the set. I got an ember in a downpour once but paid for it in blisters. Cold too is a problem - you have less thermal mass and so the set and char will cool quicker.
I hope that answers a few questions. Anything more specific - ask.
Best is for you to get a set together and practice - you will get to understand the issues involved!
posture is personal - i work with my left heel on the hearth and right foot under my butt, leaning forward over the set. The lean will help get pressure on. Sitting up will deliver less pressure.
