Saying "Only I [do X]", "Only I [like X]", and "I am the only [Y] who [does/likes X]"

Question

I've been digging through my reference books and Google searches, but I'm not getting anywhere with this.

For "Only I [do X]", can the subject of the sentence simply be 私だけは?

私だけは電車で魚を食べます。
"Only I eat fish on the train."

And could that be done with an adjective like 好き or ほしい?

私だけは天ぷらピザが好きです。
"Only I like tempura pizza."

For my final act, I'm going way out on a limb here, but how would I say "I am the only [Y] that [likes X]?" This is the mess that I came up with:

「ドルアーガの塔」のことが好きなアメリカ人は私だけです。
I am the only American who likes The Tower Of Druaga. (Or more literally, "As for Americans that like The Tower Of Druaga, it's only me.")

How wrong is all of that? Because I'm pretty certain it's not correct.

Answer 1

I think your last example's pattern is the way to go...

• 「ドルアーガの塔」のことが好きなアメリカ人は　→　私だけです

"As for Americans that like Tower of Druaga, I am the only one"

• 電車で魚を食べるのは　→　私だけです

"As for those who eat fish on the train, I am the only one"

• 天ぷらピザが好きなのは　→　私だけです

"As for those who like tempura pizza, I am the only one"

Personally, I feel like it might be better to say,「私だけだと思います」or「私だけかもしれません」instead of「私だけです」so as not to sound too dogmatic.

Answer 2

私だけは電車で魚を食べます is not ungrammatical, but だけは tends to have a contrastive meaning or the nuance of "at least", like "(although others don't do this,) at least I (will) eat fish on the train". A more "neutral" way of saying this is 私だけが電車で魚を食べます using exhaustive-listing ga.

Compare these simpler sentences:

• 私だけがピザが好きです。
  (Among us,) Only I like pizza.
• 私だけはピザが好きです。
  (Although the other people may not like pizza, at least) I like pizza.
• 彼だけが生き残った。
  (Among the 10 people,) Only he survived.
• 彼だけは生き残った。
  (Although everyone else died / Although it was tragic,) At least he survived.

It depends on what you want to convey.

Your last attempt is a perfectly correct cleft sentence.