|: My tiny trucks require 7mm bearings
That's a bit of an annoyance, because in our line of skating, the 608 bearing is the standard.
: athough I currently have sleeves to get 8mm bearings.
In this way you can at least easily get some bearings.
: I was told by an online store that any rollerskate wheels over 90a are considered indoor wheels. Is this true?
They don't lie to you. But they probably also know near to nothing about park/pool/ramp skating. The general rule on smooth surfaces is: harder is faster, bigger is faster. The limits are: harder has less grip (so you don't want to go too hard for carving), bigger has less maneuverability. So for a ramp skater, 66 mm (or even more) is good, whereas for you, 62 mm could be the better compromise. It's always about compromises. There is no such thing as the best wheel. I tried once to go along this road and learnt not to do it again. Try to optimize the wheel for your purpose. If you ride several styles, ride several skates.
: I know that when I inlined, I liked really hard wheels,
You are more limited with respect to hardness on inlines. You lose your grip earlier on inlines so you rarely go up to 99 A or above.
: I can buy 62mm 96a wheels, but they say they are indoor wheels.
It will probably work. I have to confess that I never tried figure skating wheels for ramp riding. I alway either had Powell Roller Bones or some sort of skateboard wheels. Or Kryptos for the street.