1) Do you put punctuation after et al. (in italics of course) as it already has a full stop,
e.g. et al.. Beginning of new sentence
I've seen commas, but don't know what is correct.

2) Do you need a reference for every time a repeat reference is mentioned? Is is annoying to keep referencing the same work if it is mentioned multiple times, or good as it is clear?
Some of my chapters are questioning work in 2 papers. Can I just write "Blogs et al. suggest that...." all the way through, or "Blogs's spectrum shows that.....?" For most references I was just going to write (Surname et al., 2003) in the text, is it OK to be different for these 2 references?

anyone?

1) I've only ever had to use commas, never a fullstop, so no idea.

2) I often use "Brown et al. (2006) used method1 blah blah" in my work. It makes more sense to do that if you are looking at two different papers together.

Oh and if I am talking about only one reference for say a whole paragraphy, then I wont bother to keep referencing, I think it makes sense which reference you are talking about.

According to this ... http://dictionary.oed.com/cgi/entry/50078361?single=1&query_type=word&queryword=et+al&first=1&max_to_show=10 ... it looks like you use "et al.," but "et al." (i.e. without the extra fullstop at the end of a sentence). I think it kinda makes sense that you don't have to say 'this is an abbreviation' at the end of a sentence...
As for your second point, I won't be using the (name, year) style at all - will just have numbers - but I will probably mix the numbers with specific references to that person's work ("According to Smith and Jones [21]..."). Oh, I see your point. Not sure.

Maybe I'll just have to get someone to read bits and ask.
Thanks for the et al. bit