1) I am adding the pedal (it is my first piece using the pedal
).
In my edition (Longo), there is "Ped" indication at the beginning of each bar, and release pedal indication (*) at the end of the bar. As you know, each bar start with 2 notes played with the left hand.
Question: the depressing of the pedal should be done exactly at the same time the first note of the bar is played? Or just before, or just after?
2) The piece is marked Moderato. What metronome tempo is desirable? 1/4 note = ?
Whatever markings your score has (pedal, moderato, dynamics, etc.) they are all editorial. Bach did not provide any such directions.
This prelude is mostly about overtones, so I suggest you learn to listen to the overtones (without pedal) before adding the pedal, so that you know exactly what sound you are after.
If you look at the bass voice, it consists of two minims (1/2 note) per bar. Now, go to the piano and play middle C and hold the key depressed. For how long does it "ring"? That is how slow you can get away with, since Bach wanted the sound of that minim to underly all notes in half a bar.
How fast can you play it? Jacques Loussier plays it prestissimo, and it sounds very effective. So by all means experiment. If you are sold to the idea above (that this prelude is about overtones) then you will want to play it slowly (and not too much pedal either) to hear the build up of overtones. I think that an interesting idea that may inform your interpretation is Arvo Part's "tintinnabulation" (google it). Much of what he says about it is applicable here.
Finally most of your questions will be anwered here:
https://www-personal.umich.edu/~siglind/wtc-i-01.htmEnjoy!

Best wishes,
Bernhard.