"Warm" vocals start with the singer, of course (assuming they project a 'warm' sound or at least one that lends itself to sounding warm in the track). OK, that aside, warmth starts with your choice of mic. Use the wrong mic and sometimes no amount of EQ or other processing will provide a satisfactory result.
So, mic choice... What mic are you using? Do you have access to more than one? What's the style of the track, etc.?
Assuming you've selected an appropriate mic, the next step in the signal chain is your mic pre, and some mic pre's will indeed add a warm quality to the sound. Tube mics generally add "warmth" but that doesn't mean that solid state ones don't. What kind of mic pre(s) do you have access to?
Next, compression, reverb, delays (as you mentioned in your post). These have nothing to do with adding warmth. Compression reduces dynamic range; it can help an intimate vocal sound more "in your face", or make a loud singer's vocal sound more "dense" and sit better in a track. But they're generally not used to provide "warmth". And reverbs and delays add ambience.
Oh yes, and you mentioned exciters. They generally add more presence to a sound (this being the opposite of warmth).
What will help to add warmth is EQ. "Warmth" comes from boosting low mids, or sometimes cutting other frequencies that take away from a warm quality.
If you want to do this right, forget about plugins entirely for now. I'd like to suggest that you start with an appropriate mic and mic pre that, without any plugins whatsoever give you approximately the sound you're looking for. Then, after the recording, if the vocalist's sound needs "help", look to EQ first to achieve the sound you're after.