so I’ve been meaning to come up with a good freestyle that will impress people at school(me and my friends are doing demos for classes at our school). I generally mostly work on individual tricks but i want to doing some good freestyles. So I was wondering what are the core basics that you need to have in one. thanks! 
Long Version:
The only real tips I can give you is to do flashy tricks. Don't bother with too much tech, because people think it looks repetitive. The audience at school is amazed at different things than the audience at a competition. At a competition, if you do a technical trick, people think, "wow, that was amazing...gotta try that." while people at school think, "didn't that guy just do that trick? boring..." Also, don't do tricks that look very similar to the one you just did. I performed in front of choir to help student government to film a "talent show video" to get people to join, and I did Asian pops followed by horizontal circular Eli hops. Afterwards, people told me that it was repetitive because of those two tricks. Some good tricks to do are:
Gyroscopic Flop
Eli hops(but not too many)
Revolutions
Boingy-Boing
Combos where the yoyo spins a lot
Any 2a, 4a, or 5a
Slacks
Horizontal
and more.
Short Version:
Don’t do lots of tech(a bit is O.K.). If you have similar tricks that both look cool, don’t do them right after the other. Do flashy tricks.
Oh, and a final word of advice. DON’T use a super fast song. It’s really frustrating to see slower yoyoers try to yoyo to extremely fast music. If you really have to, choose a slow song.
EDIT: And then I see your other questions. What I do is I make lots of separate elements/tricks, than figure out ways(which involve lots of yoyo twirling) to go to the next. Stitch the tricks together so that they’re smooth- try not to have any bad transitions.
I second what you say, but I would like to point out that when I was in school, people were more impressed with 5a than anything else, you may find a different result but give it a try, also 2a and smooth fluent 3a are very impressive…
And for your 1a, take into consideration that most impressive things have 2 actions going at once (two yoyos- yoyo and cw), so for 1a I use a whip for the second action and It works out nicely