I'll give you the "a myriad" one -- however, in the case of could vs. couldn't care less, although you are obviously technically correct, my version would also be accepted by many members of today's readership.
You could even go with just one comma: Thank you for your kind offer, but unfortunately I won't be attending.
As far as that goes, in these days with a trend toward minimilist punctuation, you could miss them all out and the reader would still get the gist: Thank you for your kind offer but unfortunately I won't be attending.
When I was a kid thsi would have bored me to death -- now I love this stuff LOL
Because engineers couldcouldn't care less -- if they really wanted to learn, there are a myriad books out there already...
"myriad" doesn't take the article.
Update: Seriously, many students go into engineering because they think they won't ever have to write anything. A typical undergrad curriculum enforces this notion, because most Ugrad engineering courses are all math and diagrams, with no writing.
Then they graduate and hit the real world... and they're completely unprepared for the necessity of clear, unambiguous writing in design specs and data sheets and program comments and technical articles, etc.
Solution? Hire PhDs. After writing a dissertation, the rest of those documents are easy.