Oil gilding is supposed to be easier than the water gilding but go figure I am less comfortable and good with it
Your surface needs to be dried and totally sealed, shellac is good for that
Size is applied as nice and thin as possible, also a very even layer even in the recess but be sure there is some in those bloody recess.
The size have a different working time.
On that project I used a slow size which requires an 12 hours drying period prior to gilding. I put it late in the evening and start early the next morning.
Brass is applied directly for the book
Push down gently to be well stuck on the size
Here is the video
Same everywhere, at least 2 layers on the carvings and press it well.
-- Patrice lejeune