Check with your GM.
By a raw Reading, a Ghoul is a supernatural creature, thus must be a 5 dot retainer.
All ghouls start with some disciplines. (Normally celerity or vigour or resilience at very low rating).
This also means all ghouls are incredibly competent people.
Not nesc what your game style might want.
(PC: "Igor, get the door", Igor: "I installed a automatic door last week, sir.")
However depending on your Game the GM might be willing to throw that around.
You GM might rule that you are vampires, it is expected that vampires make ghouls of most of there followers (In your setting). Thus he might say that any retainer can be a ghoul, so long as you are willing to pay the willpower point to create, and the vitae each month to maintain.
This increases the variety of ghoulish competence.
For example he might allow you to have a 1 dot ghoul retainer who is effectively mentally disabled, (which is the description of a 1 dot retainer). It may be that his blood addiction has destroyed much of his ability to think and act independently.
I've also seen the ruling, that a ghoul is a ghoul, you don't have to pay any XP for it. It is addicted to blood. It will serve you to service its addiction.
But if you don't pay the XP to take it as a retainer, then it is not serving you, it is serving its addiction. Circumstances (Story) could easily occur that sees it serving another master.
Where as once you pay the XP for it, it is an extension of your character , to a limited extent. It might still be wooed to betray you, but the GM would be thinking very carefully before doing so.
You may like yo acquire the book Ghouls, though it is in a large way focused on Ghoul PCs. It does really go into Ghouls.