'There is so many things going on in my head'. Or is it 'there are so many things......'?
'Things' being a plural, suggesting more than one, so I assume it's 'are'. However, it is 'there is so much stuff going on in my head' but 'stuff' suggests a multiple of 'things' so why is it different?
Also, I was taught to put punctuation outside a bracket, so is this correct if placed at the end of a sentence?:- (I'd forgotten all about that!).
The use of is/are depends on whether the word itself is singular or plural - don't worry about the meaning of the word. It is correct to say "there are so many things..." and "there is so much stuff...".
It gets into a bit of a grey area when using words which are singular but which refer to a group of people - eg government, staff. I think it is technically correct to say, for example, "The staff is allowed to use this room", but "The staff are allowed to use this room" sounds more natural to me. (I think American English is actually more strict on using "is" in these cases.)
I would agree that if the whole sentence is inside brackets then the punctuation should also be within the brackets, as it's ending that sentence and it makes no sense for it to be separated. If it's part of a larger sentence, then the full stop (or exclamation mark etc) should be outside of the brackets as the full stop is ending that whole larger sentence not just the bit in brackets. (Hope that makes sense!)
I think the thing about "staff" is that it's pretty unlikely to be made a plural- I can't see anyone saying "staffs", unless they were talking about sticks of wood, or about the north Midlands and had lost their shift key. Even if you were referring to all the teachers in all the schools in Stoke, you'd probably say "the staff of the schools in Stoke", not "staffs". So "staff" is always a collective noun, and only sounds right with "are". But people do talk about "governments", so it sounds OK with "is" and with "are".