spacing is very, very, very different from hitting max distance aerials and normals
spacing is something complicated you're going to have to figure out through playing people (preferably better than you). basically, "spacing" is denying your opponent a space or an option through positioning + placement. more often than not you shouldn't be aiming your attacks at where your opponent is currently standing. it's more like aiming your attacks safely at an option you think your opponent would like to pick and it kind of ties into being able to read + having an understanding of the limitations of characters.
if you're not punishing someone you don't place your moves to hit exactly, you place them in a safe place that also puts you in an advantageous spot
(i.e. if I SH nair in place as falcon and they run into to me I win. If they don't I'm safe if I placed the nair far away enough to not easily be punished but close enough to also be threatening/maintain a threat/actually stop them from doing something [like running towards me/center stage] even though I never intended on committing to hit them per say. in this basic situation, I placed my move in such a way that if it goes in my favor, it was free. If it does not, I really lost nothing. And then conditioning comes into play, then you start to exert even more pressure while making even less of a commitment once you establish that in certain instances, you will cover a good number of options/the easy option your opponent would like to take. Your opponent starts thinking "what IF he nairs here/now"? Then as falcon you could just dash dance and they have to respect your nair even though you may not even have an intention of putting one out and you're just dash dancing so now you're threatening with no commitment).
that's basically it. if they're doing something bad/stupid in neutral (like limiting their own options) then you can just hit them of course.
hitting max distance attacks is also a part of this this as it is sort of a natural extension of that idea, the blue text, but primarily, to me, spacing is more about placing your moves in a correct place and it's more about where your body is + what attacks are available to you in your current state + what can your opponent do to you in a certain range while keeping the first 2 things in account and building your game around that.
it's not poking people with the tip-tip-tip of your attacks all the time although that's is a part of it (I think the understanding of positioning precedes that and is generally more practical)
a player with great spacing is basically someone who exerts a lot of safe pressure, they constrain you without actually forcing the situation. play a good puff player, someone who understands the char, and you'll understand the feeling. puffs generally don't lean their aerials all the way into people or overtly run at people, they aren't overly concerned with hitting you where you are standing at in an instance, consider why that is.
with a character like fox I find that out of neutral I think of going about things in a manner that cuts off my opponent with a low risk on my part or makes them have to approach me. fox really has mediocre range if you think about it so his "spacing" is more focused on placing his body in the correct place imo.
I hope that answered your question but once it "clicks" everything falls into place. any comments etc.?
(also, imo, this stuff is much much more important than combos or edgeguards because you need to win neutral before any of those things happen and at that point you can learn combos/follow ups/techskill and apply them well. that's way easier to learn)
secondary stuff
lastly, literally play whatever character you want. one you think you can play in a overwhelming majority of MUs. it helps very very much to have a clear main you are confident in for a game 1 situation all the time. even if your character isn't the greatest like ICs or something they are good enough for you get everything out of the game (imo the end of the "viable" chars are falcon, ICs, luigi, pikachu, samus, doc, yoshi, ganon so any of them or anyone better is good enough to be a main). The worse your character is the harder time you are going to have but one thing about mid and low tiers is that you get really, really good at understaning the dynamics of disadvantageous/advantageous situations because you're going to have to work those a lot harder.
It's kinda all over the place lol
mid level technical characters make better mains IMO
