Punctuation within the bracket depends on (a) whether what's within the bracket is an entire sentence or not; and (b), separately, whether the punctuation is to do with emphasis (or anything else relating ONLY to the bracketed words) or simply syntax.
So, your example sentence is right - as the exclamation mark is emphasising only the bracketed words. (If you wanted to do an entirely parenthetic comment, like this, as a sentence entire in itself, the punctuation would come within the brackets. Like this.)
Shall ... when you're using the first person (I or we) the difference is to do with intention vs. objective future events. I "shall" is objective - just what is going to happen; I "will" means you are intending something. In the third person (he/she/it/they), "will" is objective and "shall" indicates a command or order (ie the third person version of intention).
As this could be all horribly confusing, the classic example to how NOT to do it is the person in the sea shouting
"I will drown and no-one shall save me!"
- ie, grammatically, "I INTEND TO drown and no-one IS ALLOWED TO help me" - which of course is the opposite of what the person means.