I don't measure it by amount, but instead on how many Bells I spend. I usually spend anywhere from one million to one and a half million Bells on turnips, depending on how much Joan is selling them for and how much room I have in my storage.
You can honestly safely purchase as many as storage and funds allow. With all of the available online resources, it is very easy to get a high price (500+) and even easier to get a price like 300 per turnip.
For the past two Sundays I've bought for 200k, but now that I have expanded my basement, I'll buy enough to fill every tile I don't want them laying around outside, so this is my limit.
I haven't bought any yet because I don't have WiFi at home. I consider it too great a risk for loss when I don't have access to the internet at all times to be able to find someone with high turnip selling prices. But I will be buying a lot when I do get WiFi access!
As many as I can fit in my closet lol
I earned around 2-3 M this week
and 2-4M last week, I don?t really remember the numbers, but I earned a **** ton, from now on I?m gonna use a second character and fill that Locker up full, I?m gonna get rich
I bought 2,900 turnips for just under 300k. And sold them all today for 950k. ^_^
Also, am I the only person to have thought of stuffing all my turnips in the museum? My house changes too often and there wasn't enough room in my storage so I lined my gyroid exhibit with them. xP
I don't usually buy turnips on sunday, because I don't have that much room.
So when Re-Tail is buying turnips for a super high price or one of friend's town is, that's when I buy.
My friend and I was using an extra DS to TT to sunday to buy turnips when my turnips were at 513~.
I just keep the price high for the rest of the day and we keep buying and selling turnips for hours and at the end we each made about 40m each, we wanted to aim for 100m, but that's a little to greedy. xD