Thanks for the welcome!
I am an American who has recently returned to the US after several years in the UK. (What timing, eh?)
Across I feel you on 'confident but concerned.' 
I have been working my tail off on GOTV efforts and many of my friends and family have, too, so I agree; I don't think anyone is taking anything for granted.
On a more serious note, I searched but couldn't find a link here to Rachel Bitecofer's midterm predictions. She is Asst Dir for Public Policy at the Wason Center and predicted last year's Democratic surge in Virginia when all the other pundits were predicting a nailbiter. Here is how she sees the 2018 elections:
wasoncenter.cnu.edu/the-battle-of-the-bases-negative-partisanship-will-decide-election-2018/
My forecast asserts that the results of the 2018 midterm cycle, especially for House and gubernatorial races, have been set in stone since just around 11pm on November 9th, 2016, when Hillary Clinton lost her bid for the presidency unexpectedly to Donald Trump. That loss cemented a considerable enthusiasm advantage for Democrats that will last the length of Trump’s tenure in the White House.
She is predicting a larger victory in the House for Democrats than basically everyone else. May it be so!