You may not get good results with this strategy. You could end up stuck with 100+ uA just to allow the system to run the tick handler every millisecond. That’s a big difference compared to 1 uA.
Using stop/standby modes is a huge help to reduce power consumption. And if you combine it with tickless idle, you can have lots of flexibility too, for when feature creep comes.
Which specific STM32 are you using? And which on-chip peripherals do you expect to use? You should find enough help here on the forum to be successful.