What are the 'correct' mini fuses to buy for the Prius-I saw there are different size mini fuses?

Well, minis come in the regular ATM and the ATM "low profile" flavor. The regular ones have their metal blades poking out the bottom, so they kind of stand up in the fuse box. The ATM LPs have the metal blades kind of continue up the sides of the fuse, so the fuses fit further down in the socket. It's easy to see which kind you've got, if you take off the box cover and look.

My Gen 3 uses low profile, but I'm not sure about Gen 2.

Regular ATMs can be used in the inside (instrument panel) fuse box, if you're not fastidious about putting the cover back on (they'll stick up too far). That's not an issue in the underhood fuse box, where the cover is tall enough it won't matter.

Planning on blowing a lot of fuses?

 

“Correct,” in my opinion, would be the Toyota parts listed in catalog Figure 84-01, Switch & Relay & Computer:

5 A (Tan) 90080-82031
7.5 A (Brown) 90080-82050
10 A (Red) 90080-82051
15 A (Blue) 90080-82052
20 A (Yellow) 90080-82053
30 A (Green) 90080-82054
25 A (Clear) 90080-82055​

And the low profile style comes in two blade widths, 10.0 mm and 10.9 mm. See the Littelfuse data sheet (PDF) and my April 2017 and July 2017 notes on the similar fuses for the fourth-generation Prius, with links to the PEC data sheets. I believe the Littelfuse parts, in both widths, are now available from Mouser and Digi-key.

Hopefully you found some that actually meet the specifications.