2 years 5 months of semi-permanent chastity now (unlocking only for shower and shaving), and 1 year before.
Main problems were finding a fitting cage, dealing with frustration first few months, and quality of sleep.
I've hanged ring shapes, cage shapes and sizes, materials... Overall changed 5 or 6 cages before finding one, that was both fitted well (comfortable for daily wear, secure), and practical (pissing, hygiene).
Most unbearable frustration was first 10-15 weeks, until learned to consistently cum from nipple stimulation.
Night erection causes huge discomfort. First 10 days was pure hell - painful rock-hard erections, that I couldn't cease, that cause me sleep in fits and starts. 2 weeks later body adapted a bit - erections become less painful, and could be ceased by gentle perineum massage. 10 weeks after I was getting only half-asleep during erections, and 2-3 months after I started to sleep normally, not aware of night erections. (All periods are approximate - that was long ago, and I don't quite remember exact durations)
The only precaution - don't use resin and inverted cages for longterm. Resin is fragile and too porous for hygiene maintenance, and inverted cages cause HUGE problems every time you pee. Beyond that it's all about body features and personal preferences.
Size reduction is temporary matter - couple of weeks of normal sex/masturbation will get it back (at least after 1 year of chastity). Also no major problems with erection: maybe a bit rare, but always stiff.
Also there was one interesting mental change - after 5-6 months, when I started to perceive chastity as a part of my body, every taking it off (for example for medical reasons) started to cause great deal of stress - without the cage I felt too naked and vulnerable, and getting huge relief when wear it back on.
Would be glad to add something else, but not sure what you want to know.