kare wa shippai o amari shinpaishinai you da ga, jitsu wa yoku junbishite iru.

ようだ marks the speaker’s inference: “it seems/appears (that) ….” It suggests the speaker has some basis (observation, context, indirect info) but isn’t stating a hard fact. It’s softer than a plain statement and more neutral/formal than みたいだ.

• Here: 心配しないようだ = “he seems not to worry (much).”

With a negative, あまり means “not very/not much.”

• あまり心配しない = “doesn’t worry much.”

If you want “too much,” use あまりに/あまりにも or more naturally 〜しすぎる:

• 心配しすぎる = “worry too much.”

Both patterns exist, but they pair with different predicates:

• Verb pattern: Xを心配する (worry about X). Example: 失敗を心配する.
• Adjectival/nominal pattern: Xが心配だ (X is a concern). Example: 失敗が心配だ.

Don’t mix them (×Xを心配だ, ×Xが心配する).

Both are fine, with a slight nuance:

• 失敗を心配する: concise, treats “failure” as a thing.
• 失敗することを心配する: emphasizes the act/event of failing.

Meaning is essentially the same here; the shorter form is more natural.

• 心配しないようだ: general tendency/characteristic (“he seems to be the kind of person who doesn’t worry much”).
• 心配していないようだ: current state (“he seems not to be worrying right now”).

Context decides which is intended.

Here だが is the conjunction “but/however,” not the subject marker. Register-wise:

• だが: more written/formal.
• が (as a connector) and けど/けれど(も): everyday speech.
• Polite: ですが.

In this sentence it contrasts the two halves: “He seems not to worry much, but actually ….”

実は is a set phrase meaning “actually/in fact,” used to introduce background, a correction, or unexpected info. The は is historically the topic marker inside the fixed expression. It’s usually followed by a comma:

• 実は、よく準備している。

よく can mean either “often/frequently” or “well/skillfully.” Both readings are possible:

• “He actually prepares often (a lot).”
• “He’s actually well prepared.”

To disambiguate:

• Often: 頻繁に/たびたび/よく
  • 準備する.
• Well/thoroughly: しっかり/ちゃんと/入念に準備する, or “be ready”: 準備ができている.

Vている can express:

• an ongoing action,
• a resultant state, or
• a habitual action.

Here it can be habitual (“he regularly prepares”) or resultant (“he is in a prepared state”). Compare:

• よく準備する: unambiguously habitual.
• よく準備している: habitual or “is (well) prepared” now, depending on context.

Yes, you can omit it if the referent is clear:

• （彼は）失敗をあまり心配しないようだが、実はよく準備している。

Using 彼 is fine, but in real conversation Japanese more often uses names, titles, or just omits the subject when obvious.

Both are acceptable:

• 失敗をあまり心配しない
• あまり失敗を心配しない

There’s no big meaning change; the first keeps the object next to the verb, the second slightly foregrounds “not much.”

Polite version:

• 彼は失敗をあまり心配しないようですが、実はよく準備しています。

You can also soften the inference:

• …心配しないようですね。