Question

Will all the bulbs have the same brightness in a series circuit no matter how many? Does it matter how many bulb there are?

Answer 1

IF all the bulbs are identical bulbs . . . . .

All the bulbs in series have the same brightness, and that brightness
depends on how many there are. More bulbs ... all are equally less bright.
Fewer bulbs ... all are equally brighter.

If the bulbs are not all identical, then it depends on what each one is, which one
was removed, etc., and it can get complicated.