"Please don't take money."
I think both are very common. The kanji way could be even more common, but it depends on where you look at.
When attached to the て-form, it is written in hiragana. When following a particle (を, in all cases I have seen) it may be written in kanji.
お金を取らないでください is not currently accepted via IME input. Forces you to use とらない.
You need to use the “-te” form of the verb to ask someone to please do something. When you have a negative verb, the “-te” form ends with “-de”, so toranai (don’t take) becomes toranaide kudasai (please don’t take).
お金を持って行かないでください - is that wrong? I understand もって行く was the typical way of saying 'take' as in "have on you while going".
I don't think many people have interpreted the sentence that way, so if you submitted an error report your answer should be added to the database eventually.
を as a particle is written as "o" using Hepburn romanization, though that might be confusing for beginners.
とらないで (toranaide) is one word, and I think it's best written that way.
Okane o toranaide kudasai.
Okane wo tora nai (or toranai) de kudasai. Is absolutely correct. It is 'wo', not o because it is used as particle here.
There are different methods of romanization, but I find Hepburn to be the one most used. In modified Hepburn, を is written as o, は is written as wa, and へ is written as e.
There is nothing wrong with writing を as "wo", but I was pointing out that according to Hepburn you would correctly write it as "o". For pronunciation purposes, I think "o" is best. For learners who are trying to understand hiragana and its readings, I do agree that "wo" is possibly a better choice.
It is also standard practice to write a verb as a unit, and it makes it difficult to read easily when you break up the verb as "tora nai de". As there are no spaces in Japanese, again, it's okay to write it that way, but when it comes to readability I think most people prefer "toranaide".