Great and fascinating thread. I have said that if I were to do over I would seriously consider 2 rail O scale. But I still like to run my my childhood Flyer so that won't happen. My comments are viewed as heresy among the S scale crowd.
Speaking of HO building here are some pictures I posted before.
The two store fronts and the red background building are modified HO, DPM and City Classics I believe.
The tan shed is a $1 bashed (butchered?) N Plasticville kit and the red one is a bashed cheapo HO kit.
Some of the S scale modelers frown on HO kits and others are more tolerant. Since my layout is more low rail it doesn't matter to me. The biggest objection has to do with brick size but painted with no mortar lines, it doesn't look that bad especially to my bifocaled and previously cataract ridden eyes.