I dunno, my style of 'lead guitar' is more like rock chord melody with a mix of truncated chords or tasty extensions with minimal 1s 3s and 5s and licks interspersed with the passing tones that support the vocal without strictly doubling much of the rhythm line, but its based on years of big band jazz experience and I couldn't coach anyone how to do it in les than a year, especially a beginner. but it would work well for what you are trying to do if you could do it....
I would interpret all the passing chords if I were you, maybe reharmonize the main chords for interest and then work out counter rhythms so you have both rhythmic and harmonics differentiation. A song is just a melody, the 'chords' are just one possible harmony and anything that works is fair game if it fits the mood of the lyric. Okay? then at show time I might throw caution to the wind and just play it however I felt it at the moment...
also, 'strumming' is kinda washy and lame, be precise, use your fingers like the guy on the left or do something to change the attack so it doesn't wash with the guy strumming away with his pick like its a boy scout weenie roast
if you want to rehamonize or discover passing tones by ear try singing or playing a couple diatonic harmonies to the vocal line by ear and then use the notes that are NOT in the main chords to generate the passing tones (off beat chord changes between the main chords) and to reharmonize/extend the chords as written, avoid ANY notes being covered by the main rhythm line as much as you can, especially 1 and 5... then you can rehearse it a few ways, put it all in the back of your mind, and then try playing it with your gut for a little and see what comes out. maybe almalgamize a few versions of your part to make an ideal line
at worst you won't get anything out of my suggestions but experience, and really that's more important than getting it 'right' sometimes
most importantly, whatever you decide to do, do it with conviction and passion because connecting with the audience is more important than musical technicalities unless you're in an orchestra performing Stravinski or something and even then passion is as important as proficiency