Learn Hardcore Japanese: watasi ha yasumi ga sukunai desu.

With adjectives that describe a property or amount, Japanese commonly uses the pattern Xは Yが Z (e.g., 私は日本語が好きです, 私は背が高い). Here, 休みが少ない is the descriptive core.
を marks direct objects of actions; there’s no action verb here, just a description.
You can say 休みは少ない, but that topicalizes “days off” (often adding a contrast), whereas 休みが少ない simply states the fact.

Is 少ない an adjective? How do I conjugate it, and what’s the opposite?

Yes, 少ない is an i-adjective.

Plain: 少ない
Polite: 少ないです
Negative (plain/polite): 少なくない, 少なくありません
Past (plain/polite): 少なかった, 少なかったです
Past negative (polite): 少なくありませんでした The opposite is 多い (“many/much”); e.g., 休みが多い, negative 多くない.

Why is です used after an adjective? Can I say 少ないだ or 少ないます?

です adds politeness to the sentence; it doesn’t change the adjective. So 少ないです is fine and common.
Do not say 少ないだ or 少ないます. I-adjectives don’t take だ, and ます attaches to verbs, not adjectives.

Can I drop 私は? What about 私の休みは少ないです?

Yes, it’s natural to drop 私は when context makes the topic clear: 休みが少ないです.
私の休みは少ないです is also correct; it topicalizes “my days off.” The meaning is similar, but it sounds a bit more possessive/emphatic about “my days off.”

What’s the difference between 少ない and 少し? Which one belongs here?

少ない is an adjective meaning “few/little (in quantity),” used to describe nouns: 休みが少ない.
少し means “a little/a few,” used as a quantifier/adverb: 休みが少しある (“I have a little time off”). Here you need the adjective 少ない.

How do I say “I don’t have much time off” or “I only have a few days off”? What about “not enough”?

“I don’t have much time off”: 休みがあまりない（です）. (あまり pairs with negatives.)
“I only have a few days off”: 休みが少ししかない（です）. The しか…ない pattern strongly emphasizes limitation.
“Not enough”: 休みが足りない（です） stresses insufficiency rather than just small quantity.

What’s the difference among 休み, 休暇, 休日, and 休憩?

休み: everyday “time off / a day off / break” (broad, context-based).
休暇: vacation/leave (formal/HR), e.g., 有給休暇 (paid leave).
休日: a non-working day/holiday (weekends, scheduled days off, national holidays).
休憩: a short break/rest during work/class.

Does 休み mean “a day off” or “days off”? How can I make it explicit?

Japanese nouns don’t mark singular/plural. 休み could mean “a day off,” “days off,” or “time off.”

To be explicit with count: 休みが三日しかない (“I only have three days off”).
To emphasize duration: 休みの時間が少ない (“I have little time off [timewise]”).

If I mean the breaks are short in length, should I use 短い?

Yes. 休みが短い means each break/holiday is short in duration. 休みが少ない means there are few breaks/days off (count). You can combine: 休みが少ないし、短い.

Can I say 休みを持っている to mean “I have days off”?

No. Use ある/ない for possession/existence with time off: 休みがある／ない. 持つ is for holding/possessing tangible items or certain abstract attributes; 休みを持っている sounds unnatural.

How do I ask someone if they have little time off? Can I make it sound explanatory?

Polite question: （お）休みは少ないですか。 Adding お shows respect for the other person’s time off.
Casual: 休み少ない？ / 休みは少ない？
Explanatory/empathetic tone: 休みが少ないんですか。 For yourself: 休みが少ないんです (polite), 休みが少ないんだ (casual).

How can I intensify or soften the statement?

Intensify: 休みがとても少ない（です）, 休みが少なすぎる, 休みがほとんどない（です）.
Soften/hedge: 休みがあまり多くない（です）, 休みは少なめです.

Any pronunciation or writing tips for this sentence?

Readings: 私（わたし）, 休み（やすみ）, 少ない（すくない）, です (“desu,” with the final u often devoiced).
Japanese is normally written without spaces: 私は休みが少ないです。 Spaces are just for teaching clarity.

Can particles be dropped in casual speech?

Often, yes. You might hear 休み少ない in casual conversation. For accuracy as a learner, keep the particles until you’re comfortable with when omission sounds natural.