I've decided that my own personal limit will be 200 items, and I'm a long way from there now. I have 108 items, was up to 115 items but had some sales, and I'm not too fast to replace because I want my shop to be a place where people (many like me) come to peek, stop, sigh, and say, "Ahhh! I really want to look around here."
For those of you who want to fill your shops and pages, remember us: the many people on here who have said too much is sometimes, well, too much...and more of a turnoff than an invitation into a shop of any kind.
Think like a buyer, and keep in mind that 30% of the world population is exhausted by overstimulation. The other 70% is actually energized by it. So if you want 100% of your potential buyers to come through the door, don't make your shop what my grandmother used to call "overmuch."
I think there's a misconception on Etsy that, if 100 items is the magic number, it must be even more magical to reach 200, or 300, or more. If someone actually studied this, I bet they'd find exactly what many of us are saying. There's an upper limit (number unknown) where too many items begins to work against you instead of in your favor.
But if you happen to be in a milieu where your shop depends on lots of items, please section it thoughtfully, and know that many of us will thank you. ;o)