Sleep and USB-C display work out-of-the-box on my Lenovo T470s running Ubuntu 18. I've even used a USB-C hub with Ethernet, HDMI, USB3, and power delivery. Just one wire for everything. Sleep has worked for years now. YMMV
what's missing to bring my private t470s on par with my work macbook is "hybrid sleep". the macbook seems uncannily smart of sleeping when i close the lid, then eventually hibernating, so that even after a whole weekend unplugged it has an almost full battery when i open it on monday.
meanwhile the sleeping t470s drains the battery by keeping the RAM alive and eventually runs out. the arch wiki has some content on this, but it did not make me hopeful to get it to work
And configure it as the lid close action trough logind conf (or your DE's).
It works differently, though (AFAIK). It saves the state to both RAM and disk, so when battery eventually runs out, you can resume from disk. The solution you offer seems interesting. It would just need a RTC wakeup event, so that the system goes all the way to S5 after a set time.
