If I cure myself from vampirism and I don't cure Serana, will I still be able to turn back into a vampire?
Solution 1:
Yes. If you've completed the Kindred Judgment quest and as long as Serana is not cured of vampirism, Serana can turn you into a Vampire Lord. You can repeatedly switch between curing yourself of vampirism through the Rising at Dawn quest and asking Serana to turn you back into a Vampire Lord, with no limits.