Rules of thumb for riding position....thats all they are, just rules of thumb....but they do provide a place to start.
These rules of thumb result from the "herd experience" of generations of cyclists....they aren't science, they aren't fact, don't waste time arguing the toss over wether they are right, wrong, or halfway between, dont try to explain them.....just use them to get started, then play around from there.
Set the saddle up first to be comfortable to pedal, then set the bars....you can't move the BB!!
1) foot position on the pedal....ball of the foot over pedal spindle, or a bit forward of pedal spindle.
2) saddle height so there is a bit of bend in your knee when the bottom foot is level
3) saddle setback....lots of people are comfortable when set up "knee over pedal spindle" ....thats all..no science...just works for lots of people.....compare with your bike you are used to....don't feel an outcast if it doesn't work for you!
4)handlebar height....I'm 65, I have my bars level with the saddle....good place to start if you aren't used to drops. You may well find your stem can be flipped up the other way to get more height.
5) angle of bars and brake lever position...I like the forward pointing flat bit of the top of the bars level, and the levers quite high on the bends, so the hoods are a continuation of that flat bit of bar, or even angle upwards....I find this the most comfortable position for riding on the hoods, incidentally it also reduces the effective reach compared to having the levers set lower.
6)Reach....the hardest bit for rules of thumb, and the last bit to work on anyway. Rule of thumb one....elbow on saddle nose, index finger brushes the back of the bar.....maybe!!.
Rule of thumb 2....when riding, the bars hide the front hub....maybe!!
You should be comfortable and relaxed, with a bit of give in your elbows. If the reach is too long, I find my hands come back to behind the hoods....too short, and I drop my neck down between my shoulders.
It will take time to get used to drops!