I've dropped my nic level several times over the years 50-40-30-20-25. What generally happened was I would vape more for a couple weeks and then kind of settle back into my normal routine. You'll notice those were all pretty big jumps. I DIY and base 10 just makes the math easier, but it also turned out that 30-20 was just too big a reduction for my system to handle so I stepped back up to 25. If I reduce it any further I'll do it in 5 or even 2 mg increments. As a couple of others have said, keep some of the higher strength around for stress, waking up etc.
ETA: On the insomnia thing, having some lower strength for night time is definitely helpful. I just made some 10 mg for chain vaping on ecf before bed