To me, the number by itself is irrelevant. It's all about how it affects your portfolio, the reasoning behind your purchase and, more importantly, your handling of volatility.
If you switch from buying <5 shares at a time to buying >100, then your portfolio's weighted heavily towards to a small number of players. If they rise, it looks great. But, if they fall, panic can set in and you start making rash decisions. This is where a lot of money can be lost.
Humans are stupid. Find a level, stick to it, and if you want to upscale then do it wisely.
Say you currently hold 5 of each, but want to start upping your investment to 100 at a time
- Reassess your portfolio- if there's people who you wouldn't by again, consider selling (though this should be standard practice already)
- Spread your investment across the remaining players over time to help keep your overall holdings balanced, rather than piling in to one or two players, by topping up the numbers you already hold by a few each.
- When you get to c.100 each, or whatever your original (carefully planned, obviously) balance was, crack on at the higher level.