i love 100 psi because its softer than your average hoop .... usually use 3/4". my first favorite mini move was double elbow bends. i think its a good one to start on, because it helps you get the feel and timing of smaller hoops. best of luck ma ^.^
I like 1/2" 100-125 psi, 20" or smaller if you want to be able to do buzzsaw (go smaller if your arms aren't long!), otherwise slightly larger makes it a bit easier to learn. It's actually nice to have two pairs, one maybe between 24 & 28" depending on how fast you like to move, & the other small enough to do buzzsaw. Moves are slightly different with the larger hoops especially as you near 30"-- the hoops tend to bump into each other a bit. On the other hand you don't have to do those surface switches quite so quickly, which can help you learn. And if you want to move onto the body, 30" is minimal in my experience-- 33" is better.
Mini tricks are REALLY hard to explain... I highly recommend taking SaFire's class. There are a few tutorials out there, but SaFire breaks everything down so clearly & covers a lot more territory.