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In regards to seventh chords the second inversion is still a no-no if its unprepared or isn't a passing chord, however the third inversion (the seventh in the bass) can be used freely even though it creates a prefect fourth with the third of the chord.

In regards to broken chords you can think of them as block chords but you also have to be careful, melody notes can not move in octaves with the broken chord, or in fifths.

Of course you can have more then four voices, heck have six, or seven, how bout ten, why not hundred? You can have as many voices as you want. The Ricecar from Bach's musical offering uses six voices, if you want a good example. Obviously with more voices the music becomes more dense and following the rules of voice leading becomes increasingly a chore, however you can have a voice or voices drop out at anytime only to have them return at a later time for dramatic effect, be creative. There's really no rule on the number of voices you can have in a composition. The rules of voice leading remain the same.

I don't really have any websites for you to learn theory from, I mostly read books for that stuff. A good place to find works from composers is the IMSLP Music Library, it's online and its free they have thousands of works from Bach to Brahms, its a great place to go if you're looking for something to study.

Hope this helps. Good luck.

Thanks PSaun! Really appreciate you replying and your advice.
So (talking piano) that means if you have a broken triad in the bass clef and then a block triad in the treble. You have 6 parts to check for consecutive 5ths etc?
 

ie 3 parts from the broken triad and 3 parts from the block chord?

Yes, that is correct.

As far as chords with more than four different notes, there are other types of extended chords with added ninths, elevenths, and thirteenths. For example, one of my favorite chords is a dominant seventh chord with an added flat ninth (5 notes), so many tritones

Edit: However, if you are talking in terms of traditional and strict voice leading, all these added tones would be considered non-harmonic tones and would need to be resolved accordingly.

Sometimes it's less important to know every specific about a rule, and more important to know the logic and severity of the violation. Using second inversion triads outside of cadences is hardly unheard of, and it is not necessarily objectionable in appropriate circumstances.