I am currently servicing my gravel bike. The last point is the handlebar tape, so I just have a good opportunity to adjust everything.
Do you have good advice on how I can place the shifters ergonomically optimal. What should I pay attention to?
And how do I get both exactly the same? I have some good experience with laser spirit level. There may be a simpler way.
I know in general it’s good to have your wrist straight when on the hoods. I tend to like my shifter’s a little high up but some folks like to have it flat, flushed with the handlebars. This might also depend how you angle your bars.
As for matching the hoods, I really just eye ball it but I’m sure there are better ways out there.
A few months ago I went trough that 
at the end I rotated bars to have drops paralel with ground and then I align shifters with the tops in a way that are full inline without any transition.
Spent few hours playing around. Having bike locked in Kickr was very helpful to get everything leveled and for testing. It was a good idea to start with drop angle and shifters after it.
Very dissatisfied with the bar tape finish. Not 100% clean, one side a bit closer to the stem than other 
OT: Mark one side with a pencil where you want the tape to end. Now measure from edge of stem to mark and use those measurements to mark the other side. Voila, they both end in the same spot. 
Alternatively, I just tape my cables down where I want the bar tape to end so if I ever remove & replace I don’t have to think much about it.
On topic: to make sure shifters are level, I put a level on the top of the stem to make sure bars are level and then put a longer level across the top of shifters and adjust as necessary. Alternative method, is to make sure bars are level with spirit level on top of the stem and then measure from the ground up to the bottom of the shifter levers, adjust as necessary.