The best online official dictionary is the CNRTL, but it does not include translations and it’s difficult to read even for French people.
The Wiktionary is also very good and contains a lot of translations, conjugation and grammar pages. (and it’s free!) (searching both on the French and the English versions is better)
People often think of the Larousse or Le Robert as references, but they are less complete than CNRTL and Wiktionary.
The Académie posts some articles about difficult subtleties of French language, but they are usually one century late, pedantic, conservative and irrational. The Quebecois equivalent also posts useful stuff (used as a reference by grammar nazis).
The use of punctuation is almost the same (except for decimal/thousand separators, which are inversed), I think this is not a problem.
I’ve heard the same from American education. However, some English documents written by other junists led me to believe otherwise. Run-on sentences seem to be a common error, but I don’t know if that’s just an ordinary mistake.
It also documents the slight differences between British and American punctuation.
I remember when Wiktionary had incomplete entries though I still find the format uncomfortable for dictionaries. I like using thefreedictionary’s thesaurus because it graphs synonyms, but it’s free as in price.
There are some classic dictionary brands like Merriam-Webster or Cambridge that are cited in online dictionaries, but I hardly use them directly.
To be precise, there is a thin space ( ) before « ? », « ! » and « ; » and a regular space ( ) before « : ». The «» quotes need a space inside. Nobody uses double space after punctuations. I think that’s all for punctuation spacing.
A lot of French people don’t know about these rules and a very few people (including me) will notice errors.