There are several different uses of dake and different meanings as well. 1) only;just;simply;merely 2) as ... as possible; whatever; anything 出来るだけ早く＝as quickly as possible
As for the second use of だけ (〜 as much/long/many as you/I/etc (verb)), note that you only use verbs for this grammar, just as you do in English:
Ｖplain form + だけ Ｖpotential form + だけ
As for other miscellaneous forms that do not use verbs, the most commonly used ones include: 〜(し)たいだけ ほしいだけ 好きなだけ
ほしいだけ as much as you want 好きなだけ as much as you like できるだけ as much as you can
I think that ex #208 sounds rare because it should be ではなく like in ex #5381 instead of でなく. I changed [ex #5378] k限定,最低の限度〕only; merely; just; but which was hardy understandable for me.
208 explanation: 彼女はよく働くだけでなく、魅力的だ。 lit. Not only does she work (well), but she's charming.
だけ also has a meaning of "as much as possible" or "to the extent of". For example in #5388. I often hear できるだけ - "As much as I can do it" or 好きなだけ - "As much as you like"
#208 seems strange to me... Can you add this to verbs?
Lots of common usages such as "not only XXX but YYY" "XXXだけでなく、YYYだ。"
First example : Lit. "She is not only diligent she is also charming"
Second example : Lit. "Do you have just the sufficent time to buy sufficient souveniers?"
I think that's almost correct, DC. But I rarely hear ３人しかないので and ３人しかないでも. I'd rather say ３人しかいなかったので、大変だった and ３人だけしかいないけれど十分 or ３人だけでも十分. It's significantly difficult to explain because this kind of sentences totally depends on personal feelings... しか 〜 ない implies negative feelings, and だけ implies positive feelings, that's that.