means “limit”, though often gets translated to “only”
ex: 「千円だけ持っている。」 means “I have a limit of 1000 yen.” or “I have only 1000 yen.” (neutral implication)
「だけ」 is a noun and 「千円」 modifies it
「出来るだけ」 means “as much as possible” or “if at all possible”
ex: 「出来るだけ勉強します。」 means “I will study as much as I can.” or “To the limit of possibility, I will study.”
「だけあって」
ex: 「留学しただけあって英語は上手い。」 means “Because of the limit of the fact that they studied abroad, their English is good.”
ex: 「安いだけあってすぐに壊れちゃった。」 means “Because of the limit of its cheapness, it broke quickly.” or “Precisely because it was cheap, it broke quickly.”
しか
means “more than”, but is used with negatives
ex: 「千円しか持っていない。」 means “I don’t have more than 1000 yen.” or “I have only 1000 yen.” (insufficient implication)
ばかり
ex: 「あのお店はパンだけ売る。」 means “That shop only sells bread.” (no implication)
ex: 「あのお店はパンしか売らない。」 means “That shop sells nothing but bread.” (implying that only selling bread is insufficient)
ex: 「あのお店はパンばかり売る。」 means “That shop only sells bread.” or hyperbolically “That shop sells an awful lot of bread.” (implying that there is a lot of bread, potentially despite the existence of other things as well)