I agree with a lot of the advice that's been said here - finish with something positive, and play shorter pieces before a Beethoven Sonata if you do one. In fact, that's exactly what I did.
I opened my Piano Dip recital with two Scriabin Préludes (9 and 16 for the curious). Of the pieces in my recital, 9 was perhaps the most indestructible and gave me plenty of chance to get use the piano. Which, in the end, was very useful as the sustain pedal had 1cm of travel from fully off to fully on

I then followed it with Beethoven's Pathétique (OK, a popular piece, but I was naive when I chose it 4 years ago...) whilst I still had plenty of stamina left to stick out the first movement.
After the Beethoven - the modern piece - Szymanowski Étude, Op.4 No. 3. It's lovely, actually, have a listen if you're short a modern piece and fancy something Chopinesque with harmonies that are a little more avant-garde but not off the deep end. It's quite a turbulent piece, so I followed it with a Bach Prelude and Fugue (No. 16, WTC I) to clear the air a little. Much in the same way that the Scherzo follows the Marcia Funebre in Eroica. If it works for Beethoven...

To finish - my own choice work - Debussy's 'General Lavine - Eccentric' from Préludes Book 2. I thought it would balance the programme off - it adds some French romanticism, has a jazz/ragtime feel to it, and puts a smile on one's face at the end.
I tried to spread out the romantic pieces separated to keep the sound different and interesting: romantic, Beethoven, romantic, Bach, romantic. If I was doing it again, I don't think I'd pick the Pathétique - probably No. 12. Just because I prefer the piece really and, as Steven Says, staying away from more-played repertoire might do one a few favours.
As for Programme Notes - read everything you can get your hands on, try to get a read of the Grove entries on the Composers whose pieces you are playing to fit the work into a broader context. Analyse the works - don't play a Fugue without knowing what the exposition is, they can (and did in my Viva) ask about it even though one shouldn't put it in the programme notes. I found three paragraphs per piece was quite good format: biography; information on piece, a little context; description of the progression of the piece. In the case of more/less popular composers, divert little space away from/towards the biography.