a. should I conform it to 24fps and then start the edit or keep it at 25fps
You would be best served by editing at the
native frame rate of your source material.
b. If I conform it, with the pull down method, I will be losing a frame every second. Will this not affect the timecode and subsequently the EDL which I have to send to the Lab.
Are you working with a 'best light' transfer with the intent
of sending a post-edit scene select EDL to the xfer house
for final color correction?
If so, that is even more reason for you to edit
at your source material's native frame rate.